In the Lustrum Press "Darkroom" book, Emmet Gowin shows how he uses an acetate mask to do much the same thing you are describing.
I think any tool you can use to make your art more effective is almost mandatory. We all have limited time on the planet, and even less time to devote to our art.
As Rush sang in "The Spirit of Radio":
All this machinery making modern music
Can still be open-hearted.
Not so coldly charted, it's really just a question
Of your honesty, yeah, your honesty.
And, if I'm being honest, I think DigiNegs should be just another forum on APUG, not banished to it's own poorly trafficked website. Seriously, what has done more to revive platinum and alt-processes than digital negatives?
Amen! And of course, Rush rules and Neil is always right!