https://psteamproxy.yuanyoumao.com/points/shop/

You don't even have to use them.
But you can buy more profile page showcases or for certain ones increase the number of things they show(up to "level 3").
Having backgrounds and other stuff is nice, but some can also be found on the steam market or can be traded for(the non-points shop versions)
Things bought at the point shop are tied to your account forever so if you change your mind thats too bad. For some, forever is a very long time. Choose wisely, or not, until you run out of points.

Use your points to customize your Steam presence or award fellow members of the community.

Learn more about Steam Points here:

https://psteamproxy.yuanyoumao.com/points/howitworks