Is it possible to use 2 video cards in the same PC?

My motherboard has slots for 2 video cards and I wanted to know what that’s for. I’ve never seen anyone using 2 video cards.

Is it to get more performance? Like, can you put 2 4090s and play Cyberpunk at 300 fps then?

I figure if the 2 slots are there, they’re meant to be used.