^^ That was a long one.
I see no harm in 30 seconds or so as it probably takes me that long to put my belt on, adjust the stereo etc I just wouldn't do it for 2-5 minutes that's all. Each to there own though.
Used to sit and warm up one of my old cars, a JDM import Impreza WRX but that was more essential with it's turbo'd engine. Also had to sit and let it cool down after a drive. Tbh I found it a nuisance.