Speculation...
I don't know about shields in specific, but most ships do not sail on the the seas while at "general quarters" or with all hatches "battened down"
However, In Sci-Fi, the raising and lowering of shields is very common. Here are a few examples:
I think the reasoning is that beyond plot points, making it inconvenient for the crew, or having some sort of outward appearance; having shields up all the time would put wear and tear on the shield generators, increase fuel consumption, expose shield modulation algorithms, make it harder to perform routine maintenance, etc. In general, a ship would only have a shield "up" when it anticipated going into some sort of combat condition.
Now, one other thing...shields in most of these universes come online and up to full strength fairly quickly (how long depends on how long the plot needs it to come up in...or how long it needs to remain in a weakened condition to allow that strategic strike). If SC were to implement some sort of penalty for keeping shields "up" all the time, they would also need to create some sort of mechanism to allow the shields to be raised to full strength fairly quickly. This can be done by having the shield in some sort of "standby" mode where everything is powered up and ready to go with only one or two generators down for routine maintenance at a time for the largest ships. If the shield was "off", then it might take considerably longer for the shield to come up to full. Most ships would only have shields fully down while in cold shutdown in port or when repairing major damages after a battle and they won..but lost most systems in the process. In this case, shields would be brought back up as individual generators are repaired.
Again, in most universes, generating the field is easy...what breaks down the shield is the overheating that occurs in the shield generators as it tries to absorb/dissipate/regenerate the hits being taken. In some universes, it takes just a few minutes of non-combat for shields to come back up to full. In others, it takes much longer for either repairs to shield generators to take place, or to re-charge the...call them shield capacitors or shield banks...what replenish the shield's energy after being hit.
I think this is why there was a reference to "being caught with shields down". The Idris was in "safe space", had no indication of a hostile force, and was running in "normal configuration", shields down. This may be indicating that in the future, raising and lowering shields will become part what ships will need to do prior to going into combat or immediately upon detecting a hostile or unknown force.
I don't know about shields in specific, but most ships do not sail on the the seas while at "general quarters" or with all hatches "battened down"
However, In Sci-Fi, the raising and lowering of shields is very common. Here are a few examples:
- BSG - Set condition 1 throughout the ship
- BSG TOS - Positive shields (lowered armor plates across vulnerable areas?)
- Star Trek - Raise shields. In fact, raised shields (beyond navigation shields) in the ST universe can be considered a sign of aggression. Also, review Wrath of Khan. The Enterprise took so much damage from the Reliant specifically because they did not raise their shields when they should have.
- Star Wars - Raise, set, or angle the deflectors or deflector shields. In some cases, you set your shields to cover specific areas while leaving others vulnerable (set deflectors to double front)
- Dahak series (books by David Weber) - operating a shield was only done when needful because of the power requirements.
- Robotech/Macross - the shield barrier and pinpoint barrier was only used in times of combat
- Stargate - Shields used a lot of power. Shields were depleted when the source generating them were exhausted, so they used them only when needed
I think the reasoning is that beyond plot points, making it inconvenient for the crew, or having some sort of outward appearance; having shields up all the time would put wear and tear on the shield generators, increase fuel consumption, expose shield modulation algorithms, make it harder to perform routine maintenance, etc. In general, a ship would only have a shield "up" when it anticipated going into some sort of combat condition.
Now, one other thing...shields in most of these universes come online and up to full strength fairly quickly (how long depends on how long the plot needs it to come up in...or how long it needs to remain in a weakened condition to allow that strategic strike). If SC were to implement some sort of penalty for keeping shields "up" all the time, they would also need to create some sort of mechanism to allow the shields to be raised to full strength fairly quickly. This can be done by having the shield in some sort of "standby" mode where everything is powered up and ready to go with only one or two generators down for routine maintenance at a time for the largest ships. If the shield was "off", then it might take considerably longer for the shield to come up to full. Most ships would only have shields fully down while in cold shutdown in port or when repairing major damages after a battle and they won..but lost most systems in the process. In this case, shields would be brought back up as individual generators are repaired.
Again, in most universes, generating the field is easy...what breaks down the shield is the overheating that occurs in the shield generators as it tries to absorb/dissipate/regenerate the hits being taken. In some universes, it takes just a few minutes of non-combat for shields to come back up to full. In others, it takes much longer for either repairs to shield generators to take place, or to re-charge the...call them shield capacitors or shield banks...what replenish the shield's energy after being hit.
I think this is why there was a reference to "being caught with shields down". The Idris was in "safe space", had no indication of a hostile force, and was running in "normal configuration", shields down. This may be indicating that in the future, raising and lowering shields will become part what ships will need to do prior to going into combat or immediately upon detecting a hostile or unknown force.