I cut my floricanes immediately after the the last raspberry is picked. I believe that it allows more sunshine and energy to go to the primocanes that will support my next years crop. Also allows better air circulation and reduces the chance of getting a virus in the plants. I don't see any up side to letting them linger. Maybe blackberries are a little different.... I don't know.

It will help plant more if remove spend canes now. When I pick last fruit off same day cut spend canes off. In September zone 8b primocanes grow fast until about October 20th growing at 4 inches per day all buds a lot can happen in 45 to 50 days I pinch out buds to stop longer growth up to Oct. 1st. that ends my pruning until next year when remove spend canes, In spring top new canes as shoot up above floricanes some lateral need buds removed.

All three of you are correct, but it's not worth the risk to keep them on. Yes they do supply food, but again it's not worth keeping them for the stated reasons posted by others.
I left berries on my raspberries, but cut them down as ripeness slowed, and the canes became brittle. It did produce about 200, so leaving 20 or so was no big deal.
I could see the primocanes were weak being unable to find light till I removed the florocanes. Fall buds are on the Everbearing primocanes already. They grew 6 feet tall trying to reach over the florocanes. Hopefully they will have some lateral growth now. Yeah this year the florocanes grew all kinds of lateral growth for the 2nd summer crop, I would not forgo that crop ever again. I got 200 berries off of 3 canes. I suspect these primocanes next year will do the same, but they are a lot taller, I'll probably get 300 off the 2nd crop next summer. Plus I have 5 canes now! I have 15 other plants too :) (put in this year).

Thanks guys. There isn't much disease pressure on them here (so dry all the time) but I wasn't even thinking about light competition. Cut them out yesterday...

I know the common advice is as stated above, and I buy into all those reasons, but I will throw out a contrary practice that has served me well for years.

I cut the old canes out of my summer raspberrries in late fall or even early spring when I thin out the primocnaes before bud break.
I find that I can do alot of damage the new canes leaves as i pull out the old stuff, thorns shredding them or accidentally bending them....
I also find it so much easier and faster to move through and pull the old stuff once leaves are gone.

Does it effect my harvest...I can't say for sure. All I know is that there are always all the berries we can eat fresh, freeze and jam plus loads to invite others to come pick...hard to imagine the canes holding anymore fruit.

That is true, but post-harvest canes can be pruned out in one-foot segments, reducing the pull-out damage to primocanes.

In urban areas such as mine, the curbside yard debris roll carts require the segmenting of most lengthy debris.