When I was much younger... I would ride (solo) from Virginia to Texas and back at least once a year. Always ran into a little rain here and there. Always either eventually ran out of it, or it was coming at me from the side and didn't last very long. Still, I got a little wet... and then a few miles down the road I was dry again. Never, ever, considered rain gear.
Well, in 2012, when my oldest boy and I decided to ride our bikes from Alaska to Texas and back, I still had never considered rain gear... and the forecast along the way didn't look to be all that threatening. Boy was I wrong. About 4 hours into our first day, we started getting a 'little' rain. Then, it turned into a 'regular' downpour. This is where rain gear would have been real handy, as for the next 10 hours, it rained non-stop. In those 14 hours from home to what became our first stop... we had only covered 420 miles. We were soaked, and a little hypodermic by the time we pulled in for the night.
The next day we stopped in at Whitehorse, YT and purchased some rain gear. Never had to use it the rest of the 3,580 miles... even though we had a few sprinkles along the way.
On the return trip home to Alaska, I had my Wife riding back with us. Now we all had rain gear. As we were transitioning into New Mexico, it was very obvious that just ahead was a large thunderstorm. So, we pulled over in 110°F and put the rain gear on over our leather jackets and chaps. Quickly got back on the road so as not to explode from the heat building up, and wouldn't you know... after about 30 minutes on the road, the Storm had passed before we could get into it and all we had to ride through were the wet roads. The humidity was crazy, and just added to the Heat Stress our bodies must have been experiencing. But when we could, we pulled off the road and shedded the rain gear.
The rest of the way home, we had clear skies all the way. It was an awesome trip, and I would have to say... it's better to have it along with you and never need it, than to start out and wind up riding for 10 hours straight without, it in a downpour.