Why the need for the flaps? (Alien: Isolation)

All right, allows you to open previously closed doors, then the plot will be required, for example to open a passage into the vent, otherwise you won't pass further, and in the beginning of the game all the attention they can not pay, but glue but the stuff in these rooms there is nothing

Sometimes they need to make noise to attract enemies, others off camera or alarm. The most useful door.

It's through them the fog..

To turn off the light, turn off the air supply(there is a haze in the air), disable cameras, disable the sound alert of the dangers, open doors\ventilation.