Having a stain & fiber protector applied to your rug gives you an extra window of time to treat a spill.  It can also allow for more soil to release when you vacuum when compared to non-protected rugs.

Professional application of protector to a new or freshly cleaned rug will ensure the ideal result.  The product should be thoroughly groomed in to make contact with each of the fibers and allowed to completely dry in a temperature controlled area.

There are two types of protector: solvent based and water based.  In general, solvent based fiber protectors perform better than their water based counterparts, especially on natural fibers like wool, silk, and cotton, but they both essentially help protect the fibers from absorbing a spill too quickly.  

Remember that protectors, even when applied professionally, do not make your rugs bulletproof.  The protector will help a spill bead up and sit on top of the fibers for up to 15 minutes, but you still want to treat the spill as quickly as possible before it begins to seep through the protective treatment.  If the spill does manage to seep through, you will need to have the rug professionally cleaned for your best chance at complete stain removal.

You must still maintain your rugs with regular professional cleaning in order to keep traffic areas clean.  Stain & fiber protector should be reapplied after each professional cleaning.