I've done it when I've planned an early run. It mentally commits me to doing it, and as a faffer, saves about 15 previous minutes in the morning when I'm dopey and forgetful. All I need to do is have a drink and put on things like the trainers waistbelt and earphones and I'm out of the house quietly 10 minutes after my alarm woke me which minimises waking small people up and activating their demands for breakfast.
The clothes are all clean. It's not any hotter or sweatier than pyjamas, and they'll get sweaty and muddy and I'll have a shower in the end anyway.