Auto gaining is very dependent on the way it is done. I switch it off in all software, always.
I run all my tracks through Platinum Notes, which uses a very good algorithm to adjust the gain of all tracks to the same level. After that, auto gaining in software or players is no longer necessary.
That said, you should ALWAYS keep your eye on the level meters when you are cueing up the next track and use gain/trim knob to adjust. After all there is volume level and there is energy level and dynamic range. Play a 3dB dynamic range high energy dance track with a -12,5dB gain setting and a nice 60dB dynamic range variable energy classical piece at the same gain setting and the experience for the listener will be very different from a “loudness” perspective.
As usual in DJ-ing, trust your ears!