Okay it only makes sense if the pizza was already a square/rectangle. My dad makes rectangular pizza and gives us square slices. But didn't OP said how you cut the CIRCLE pizza?
smaller slices means it's easier to handle and dip with, if you choose to do that. plus since it's like about 3-4 square slices for 1 triangle slice, it can give the illusion of eating more than you really are as well
biggest "downside" as mentioned above is you always end up with slices that are *just* the crust, but tbh, I love those. just give them all to me
Here's what a square cut circular pizza usually looks like. It's most often used for larger pizzas since triangle slices of this size would be way too long to hold comfortably. Just thought I would put this here since some people are wondering how you would even cut a circular pizza into squares.
Really it just depends on the size. I usually get smaller pizzas myself, so triangle slices are much better for me.