In reply to climbercool:
sure but they will get stronger, but will they get as strong as if you use smaller holds.
Not in my experience, especially if your feet are on the floor.
really??? I dont think fingerboards make holds small enough to actually hurt your skin. I have climbed many routes where 1 or 2 tries is all i can make before my skin is gone but I have never had the slightest skin pain from a fingerboard session, and i have spent a lot of time fingerboarding. Also if you are getting pain from crimps why not use the slopers instead of adding weight?
It gets more painful if you add weight, larger load through a small surface area, you'd crimp regardless of pain if you are training crimp strength, no benefit of training on slopers unless you're training for slopers. swapping one for the other is a completely different exercise it's like swapping a squat for a deadlift.
At the end of the day specificity and consistency are key with training, train the grip you are trying to train and by either adding or taking weight out of the system you can ensure each session is of a consistent difficulty and therefore make progressive overloads to ensure development.