Hard Reset question

[pbeaul]

This is my first smartphone/win mobile phone... and I'm curious if a hard reset will always bring it back to "stock" configuration?

Say we did have the HardSPL (whatever that is/does) with custom roms installed, would a hard reset clean everything back to the original stock rom?

Say we SIM unlocked the phone, would a hard reset affect that?

I guess, I'm just curious how "adventurous" I can get... trying to figure out how comprehensive the safety net is should I ever need it.