I have 2 positive experiences with premium processing.
If you have any urgency or you feel safe with an valid status document instead of waiting for approval and you have $1000/- to spare, then premium processing is the way to go.
If you have sent all the required documents,You can be almost guaranteed of a reply mostly approved petitions within 15 days. In most cases the approval is given with 4-5 days while the physical document takes 15-20 days to be received. The status of the petition can be checked at anytime through the BCIS website at
https://egov.immigration.gov/graphics/cris/jsps/caseStat.jsp or through the immihelp.com link.