I just don't feel right if I don't have a few rods in my auto at all times, ready to go. I will often go fishing during my lunch hours, and then maybe again in the evenings. I usually have 2-3 fly rods in the car, all rigged up and ready to go. Rods up to around 9' fit perfectly in my vehicle, so I don't even have to break them down. I haven't noticed any damage to the rods, reels or fly lines. Over time, the mono leaders or tippet need replaced, but that's a normal thing to do anyway.
I'm sure the sunlight affects the rod and lines somewhat, so I certainly wouldn't tell anybody else to leave their gear in their cars. I've been keeping at least some fly rods in my car for at least 5 years, and still use all the rods each year. The only time the rods come out for any length of time is during the winter, when the ice-fishing gear gets put into the car instead.
Someday maybe the rods will be damaged enough that they will need to be repaired or replaced... and they will have earned every minute.