Use of Manual Resistance Training?

A question for those of you with experience in this: do you find manual resistance training useful, and how do you typically choose to incorporate it into your programs?

as in pushing down on your right hand with your left and trying to "curl"? I don't know, but bodybuilders use that to pump up before they go onstage sometimes I think.

What I mean is something like towel rows. You have one partner with their chest against an incline bench and holding the two ends of the towel while the other holds the middle and provides resistance using their own strength. The technique is the same as you'd expect for a row and the idea to provide maximum resistance through the non-rowing partner's strength.

Or also using one's hands in leu of a towel doing triceps, rear delts, neck, etc.

I couldn't find a good video example but the basic idea is covered here: http://www.speedandstrengthcoach.com/Manual_Resistance_Intro.html(Work and Family Safe)