Op-amp outputs as power sources
Generally, no it is not sensible to use an op-amp for a power rail. The main reason is stability. Op-amps are typically not stable when driving large capacitance loads. If you do decide to do it, you would typically add a resistor between the op amp output and the bulk capacitance for the rail. This will likely make the op-amp stable but will degrade transient response and make the output voltage dependent on the load. In some cases that might be OK. For example if you are driving circuitry with load that doesn't vary much and doesn't need a lot of bulk capacitance. You cannot use feedback to compensate for the drop across the resistor. That would defeat the stability benefit of having the resistor in the first place.