I think i may have said this once on this forum.
To be honest, its not a choice for me. I just have noticed my fasting numbers start to drift up or down, and that means i need more or less insulin. I don't say "Oh summers here, time to go into summer mode" and lower my rates lol I just start waking up with lower and lower sugars so i have to drop my basal lol
It may be because in the summer we all try to loose a bit of weight, and try to be outdoors and more active, or perhaps its just caused by hormone levels in our bodies ? Like a hibernating bear awakening from a winters sleep lol