The main problem I had with weekend coverage was while at the last place I worked at before my own private practice, I'd walk in to inpatient and several of the patients were all on the wrong meds. E.g. psychosis-Citalopram, or malingerer who wants to be in for 2 weeks so the weekday doctor was letting the guy in stay in for weeks.
I've worked for competent institutions where they'd get rid of doctors doing poor practice like this so if I did weekend coverage it was extremely rare to see this type of thing, but at the last place? It was every freaking weekend.
While one could just say "screw it," I'm making money, this could be a liability issue cause your name will now be attached to this patient's case. Further if you try to make any abrupt changes to a case you find bogus, this could stir a lot of political pots in the department.
I remember one day I came in and I discharged 9 patients in 1 day cause all of them were clearly bogus. I was very much ticked off cause as we know discharges are A LOT OF WORK.
I remember while I was at Lindner Center and U of Cincinnati, most of the inpatient doctors would try to be nice, work as a team, and try to do all of their discharges by Friday so the weekend doctor didn't have to handle it, or if there was to be a weekend discharge do everything needed such as the discharge summary minus the last day before discharge, and call me or leave me a message to the effect of "sorry, you'll have to do this discharge but I did pretty much everything. You just have to sign the note and write how they did the last 24 hours." Last place I was at? No. Too many incompetent doctors.
So the issue is not just the money, but also the quality of treatment being provided at the place.