I know a few people that just like to just go fast for little work, like the VIP session Carl mentions. I don't really get it, from an endurance point of view, of going 50kmh but at 200w. Yes you get to feel the speed, but its at a pretty relaxed effort. There is value in going faster than you can go on your own, but I think there is more value in trying to hold it yourself once you are there. I realize we are getting a lot deeper than 'what gear should I use' lol.
Speaking from how the national team here trains, which is almost every day, lately they have been sharing the track between endurance (TP) and sprinters since its too cold outside and world cups are upon us. I don't think I have seen the TP use the moto even once, they usually just do a flying start to 'save their legs'. On the other hand, just about every single effort the sprinters do starts behind the bike (other than specific F200 practice or standing). Sometimes they will stay behind the bike but he is doing 70kmh+ and they ALWAYS try to come around it at the end. If you are not coming around the bike I don't know what you are training for, because that is how you win a bike race
Also as a side note, they always have the front disc on (rear being a boxed training wheel). Not for the speed, but rather the sensation.
Ive seen the JR and development teams do TP behind the moto, but its rare and for the purpose of feeling a higher speed for the first time I think.