If entrance reducers aren't causing traffic jams even on nice days during a flow, the hives aren't very busy.
I took them off two years ago and I noticed that the majority of the bees still used the 3-4 inches where the reducer was. The rest of the entrance was left empty. Yes we are in the middle of our flow now and there can be a little bit of a traffic jam but the bees figure it out. This is on my bigger hives that are 5 boxes tall right now(may need to add another box this week). The main advantage of leaving it on is that I don't have to worry about robbing except on some of my weaker nucs. I think it also helps keep the SHB out of weaker hives.
Gunny-T its in the mid 80's here now and they are bearding now. A larger entrance does allow them to circulate the air a little better to cool the hive. In your neck of the woods you may want the reducer off. I think the bees will do fine either way.