What exactly are PCT's for?? Your health or to keep gains?

Im sorta confused about what the use of PCT drugs actually do to a persons body, whether muscularly, sexually, or hormonally. I have read the articles on this website about PCT, and get the impression that their main use is to keep gains. Is this their main intention? Are these drugs (clembuterol, clomid, nolva) actually healthy to take after taking steroids? Or are they considered manditory mainly to help keep muscle gains? Do they have any side effects themselves- both short and long term? Or are they completely neccessary to bring back the bodys different levels?

If someone could take a few minutes to explain in detail that would be greatly appreciated.

im no expert but i believe pct's are for returning the bodys natural test levels,which in turn help u keep gains..
the clen would be more for an energy and motivation boost when the cycle is over and ur strenght begins to diminish..

for both.

both