We can also speculate about the security armor. It needn't be strictly our-world equivalent of Kevlar protection against blunt force impacts or projectile damage.
Star Fleet armor may have some energy dissipation effect, providing protection against directed-energy weapons. It may have forcefield properties as well. Who knows what else?
I don't know sometimes. People complain about the crew flying all over the bridge. Then we see lap restraints built into the seats to address the problem. And then we don't see the lap restraints again.
People complain about the redshirt deaths. Then we see armor and helmets to help alleviate the rampant redshirt bloodshed. And then we don't see the armor again.