parole based upon I-485
application for EAD & Advance Parole are based upon the filing of form I-485, permanent resident application. Once the I-130 (or I-140) and the I-485 are filed, the applications for EAD and Advance Parole may be filed (usually, but not always, simultaneously).
The advance parole will permit you to return to the US and maintain the permanent resident application.
Normally, an applicant is considered to abandoned his/her permanent resident application if he/she leaves the US without an approved advance parole.
Unless you are in proceedings, the INS does not care if you leave the US, only if or when you try to return.