getbit/setbit allow you to use a single number variable as a mini-array of values. You can store up to 32 boolean values (0 and 1) in it. And then send this variable with multiplayer plugin.
Let's say you need to send the information of which buttons on the keyboard are pressed. Normally you would need a dozen or so variables for that. But with getbit/setbit you can encode them all into a single number:
Then once the peer receives this number, you can decode it using getbit expression. For example, to check if the space key was pressed on the remote host - getbit(keysVar, 4)=1