For your location, we would recommend leaving the insert in place year round, maybe cracking it a bit if you get very high temperatures with high humidity in the summer time. The most important thing for you to consider is preventing too much ventilation from occurring in the winter time.
Leaving the insert in place also has that added benefit of mite surveying. If you put a little bit of cooking spray on the insert, the mites that fall through the screen will get stuck to the insert, and you can get a good idea about mite density in the hive without having to open it up for inspection.
I hope this helps!
Rebekah + Bee Thinking