This question already has an answer here:
Simple point & shoots don't produce RAWs, they produce JPGs. Let's assume you have a modern P&S which shoots 16 megapixels maximum in Super Fine, Fine and Normal JPGs.
First side question is if you use maximum quality, maximum size, how big prints you are safe to get out of the camera?
Main question is if you don't want to print posters what is a good compromise in image size and quality of which normally used, smaller print sizes will be undistinguishable from the original?
Eg. 4 megapixels instead of 16 but Super Fine. Or stay with 16 megapixels but reduce quality from Super Fine?
Edit: Shutterfly does not recommend more than 8 megapixels even for their largest prints. Is it maybe because their printing technique might not be that advanced?