I've been out of operational controlling for many years but back in my day I sometimes put an aircraft on a track, usually DCT to a specific point, but sometimes also to fly an offset to that track for separation purposes. From the controller perspective I would suggest (nothing has changed in the intervening years), if it suits the situation, use the technique. As pointed out earlier, not all aircraft are able easily to set up a TRK to a random point so don't use tracks if any of the aircraft are unlikely to be able to do it easily. Never had any problems either if an aircraft requested a particular track and I vectored other aircraft on headings - that said, I didn't do all this in high density traffic, but if it's that busy I would expect aircraft to be following defined routes and I wouldn't be doing any vectoring.