It mainly depends on the function of the circuit and the connection mode of the front and rear stages, and the capacitance of the capacitor is also an important judgment basis.

It's hard to make it clear without sending pictures.

Generally speaking,

If your single op amp is connected to a half-wave rectifier and the capacitor at the output end is grounded, it is generally used as a low-pass filter to filter the steamed bread wave after half-wave rectification into DC.

If a capacitor is connected in series at the output end, the effect is differential. Using the characteristic that the voltage across the capacitor can't change suddenly, the signal output by a single operational amplifier in the first half or the second half period is changed into the AC signal in the second half, that is, the purpose of shaping the waveform is because positive and negative AC signals are needed in the later period.