In the summer, I carry Frog Toggs with me when I backpack, and mostly I wear them for warmth on cold mornings when I am eating breakfast and breaking camp. I have also worn them at the laundromat when every other stitch of clothing was in the washer or dryer. As long as it's warmer than 60 degrees and not too windy, I find that I'm happier hiking in the rain without rain gear. If it gets crazy windy or if the temps drop to the high-40s or low-50s, then I think about whether I'd be happier wearing rain gear which will be hot and wet or not wearing rain gear being slightly cool and wet (sometimes I just want to flip a coin to decide on which is worse).
In October, I carry a proper Goretex anorak with me as there can be a real risk that there'll be 35-degree temperatures, rain and a bit of a breeze. That combination of conditions can be deadly, so I like to have a good jacket with me.