Max buyin = maximum winning potential, max risk
small buying = less winning potential, less risk

I used to buy in short when I first started, to build my BR and to make sure I kept it tight.

But you hate the times that you're sitting with a small stack and hit a monster, with someone else betting into you.

You just have to find your comfort zone. It's always recommended to buy in for the max, but I know other successful players that buy in short as well.