I just bought a few plants that already have berries on them. Should I pinch off the fruit to better encourage bush growth?
Yes. Leave a few to taste if you like, but be prepared to net it or the birds will get them!
It's a trade off. It won't hurt the plant to leave them on, but will slow growth. Do you want a full size mature bush sooner, or are willing to accept lower yields for the first few years to have some sooner? Your choice.
The first year I think it makes sense to pull them off........or just clip them off. The second year you can leave some one.........after that just thin out the blooms to maximize size and yield.