This ^^^
I used to do a 5 to 10 minute hot washcloth warmup when I was very very newb, and nothing wrong with it, but (if I count showers and hot tubs too) spent probably 98% of my PE career doing exactly what DLD just described. It increases pliability (yielding, suppleness) somewhat by working out some of the micro-adhesions trauma of the last session (tearing down tissue on the micro level is how you influence it to change itself, massaging those adhesions back out is how you free it up faster to be able to) , and it gets more bloodflow going.
There was an article from last year that said if you warm body tissues up to a range of heat between 104 and 115 degrees Fahrenheit then the tissue's collagens become easier to manipulate, vs an unwarmed state. That probably is better, but not doing it is a proven path too if you don't have the time or facilities (sink, bath, hot water, privacy, etc) available whenever you want to get in a workout. DLD had just mentioned a past member recently who did a lot of his length work while driving a truck, iirc. More opportunities for more workouts (and then some occasional time off too) is a common theme in PE success stories, so definitely don't let inconvenience of a 'better way' hold you back by limiting the frequency/amount of work that you actually get in.