An antenna tuner colocated with the transmitter may be required to prevent transmitting into an SWR higher than the allowed specification for the transmitter, or if the transmitter might overheat or "fold back" Tx power if the SWR is too high.
However, if one is using a small QRP or QRPp rig that can transmit into a very high SWR (even a completely open or shorted antenna connection) for extended periods without exceeding the output transistor(s) specifications or thermals, is there a reason for still using a transmitter colocated or built-in antenna tuner to lower the SWR into the feedline to the (perhaps badly mismatched random wire) antenna.
e.g. might some configurations of antenna tuners act as a bandpass filter to improve receive dynamic range, or reduce the potential for wideband receiver overload, etc., when adjusted for lowest SWR?