That's a very broad question, because Python can do literally anything in Maya.
You can use it to create a new tool that does some particular thing you want to do, like manipulate the UVs of what you have selected.
You can use it to write simple scripts that automate repetitive things. I once used a script when I was modelling a zipper; I created one tooth and animated it along a path. My original goal was to play one frame, create a copy of the tooth, repeat. After about two dozen back and forth clicks, I realized I was going to need about 500 of these things, and it was going to take all night. Spent ten minutes making a quick script that automated 'one frame forward, duplicate current object' five hundred times and deleted the few extra ones created.
But, what it really boils down to, is you can use Python to do anything you could do by hand that doesn't take human-level decision-making capabilities.
