If you're on the path, let it run. If ATC ask for a speed then do something about it. If you're fast you can either stay on the path and slow down with a bit of brake or you can use VNAV speed which will put you high, needing brake to stay on the path. Either way... you need the brake (or if you're slow, thrust). A pitch and thrust will give you a speed and path. The Airplane doesn't care what mode you use.