Yes and no! It depends on your specific amp and the phase of the two channels. This works by plugging your instrument into ch 1/input 1, then running a small jumper cable from ch 1/input 2 to ch 2/input 1. This allows you to effectively operate both channels at the same time. You are adding TWO gain stages to your sound (both triodes of a 12AX7). You are also able to utilize ALL volume and tone controls to shape your sound.
In a stock 2 ch reverb amp, the two channels are out of phase with each other. Jumping them together does not work well, as they will cancel each other out at different places on the volume knobs. If you put the normal ch through the reverb & vibrato circuit, this put both channels in phase, allowing you to play both channels at the same time.
Stock two channel non-reverb amps are already in phase, allowing the jumper method to work.
You can also achieve the same effect on stage using an A/B/Y pedal. This allows you to choose between either channel or run both at the same time, with the convenience of hands free footswitch selection. This works remarkably well in amps that have the tweed mod in the first channel!