15s vs. 17s

I've searched and not found.

So why is it that 17 inch wheels have gotten so popular? Is there a performance advantage?

I am looking to get new tires and wondering if I should get the 17" version and save for some wheels.

Thanks for your opinions.

more room for disc conversion? I prefer 15" less rim to bounce off rocks.

Most guys running 17" rims are running 37" or taller tires. The larger rim for taller tire sizes reduces the tire side wall size. The smaller side walls work better in off camber situations and when the tire is under side loads. The tire resists rolling sideways on the side wall better.