The backside making direct contact with my anus is why I wear it.
Thongs and strings make my anus horny as fuck. Squatting and feeling it ride up even tighter makes me go crazy.
As long as it's not too tight or cheap material it's not really a problem. It usually only gets uncomfortable after wearing one for a while, and usually the discomfort is kind of higher up your backside. Most of the time it feels like wearing nothing.
I only wear one if the rest of my outfit calls for it; if I have clothing that's thin/form fitting material that would show the seams of normal underwear.