My two cents.
For me, when I do my usual swim, bike, run, weights routine, I don't get sore, even when I change the intensity. However, when I do something new or something I haven't done for a while, I am sore the next day. I did yoga last night for the first time in a while and I am sore today. And, as I get older, it just gets worse. I know that if I go on vacation and don't do my weights, I am going to be sore the next day after I return.