if you do a reset factory setting (or do a wipe) then you will lose your settings and contacts and other system data. or if you rooted then installed another rom, then most likely you will lose system settings (i.e. you have to reinstall apps and restore contacts, sms, etc etc)
BUT if its just rooting, then you will not lose anything (except the warranty for the phone since rooting sort or voids warranty BUT can easily be switched back to non root later if needed)
btw, may cellphone section tayo. dun ka post next time if cellphone related ang tanong