It will make your fruit bigger.

OK, well fall bearing bear on the end. Unlike blackberries, raspberries seem to grow lateral branches just fine, so it wouldn't really help there. But it may give you bigger berries, yes. It will not hurt anything. And maybe some cultivars would grow better laterals. I have only been growing one fall bearer, I added some more this year.
You could also grow cultivars that are smaller like Fall Gold. It rarely get's over 3.5 feet. Great taste too!
I wish i had a problem with a long growing season!