Got to figure that you're doing the right thing if you're getting a warm-up done before you get out there and go full speed. Even a quick jog to get everything up and running is much better than "playing into" a match from neutral.
I'd say that the no-brainer portion of the answer is the idea of maintaining better general fitness, but anyone with "a life" may have some difficulty with making the time aside from actual tennis to take care of that. One key to my personal fitness success has been getting out to pedal my bike for a moderate ride at least twice a week (45 mins to an hour). If I do that, my 46 year old legs feel like they did in my 20's when I'm on the courts.
I've also become a believer in the advantage of getting in a thorough stretch immediately after my court time. That means stretching even before I get in my car for only a 15-20 minute drive home. Along the same lines as the cycling, that immediate full stretch has been a big plus for me when I've remembered to do it - my legs and back are always much less grumpy when I roll out of bed the next morning. By the way, I like to routinely get a basic stretch done before I get into bed, too.