What stars give good photometry?
The overall philosophy of the package is to tune the system for those stars (by far the majority) which can give excellent photometry. We don't attempt to deconvolve stars out of the wings of bright objects (even if you do it right the photometry will be poor), we simply assess whether the effect on the photometry will be larger than the normal error bar, and if it is, flag the star. This doesn't mean the code is shy of crowded fields, though. Because the optimal extraction emphasizes the flux in the middle of the stellar profile, stars have to be very close before they affect each others photometry.
Similar caution leads us to flag anything that he have the faintest suspicion about (even stars on well patched bad pixels).