The idea that you should never use the forward assist because if the round doesn't chamber you probably don't want to shoot it anyway is a valid point for range shooting. However, if you are not range shooting, you might HAVE to use the forward assist to chamber a round because you are shooting for your life. I seriously doubt that I would ever be in that situation, but it is nice to know it is there if needed.
You can't always just stop shooting and sort out the problem. One option of course is to simply run the action and eject the offending round. But what if the next round does the same thing ?
When I was in the military, I had to use the forward assist a number of times in training (never served in combat). I suppose I could have just said that my rifle was malfunctioning because there was sand in the action, but, you fight as you train, so I just hit the forward assist and kept firing.
It is also nice to know that the bolt is fully forward when you load the rifle. I think it is a good habit to get in to. And, as was already mentioned, it is a nice feature when you are press checking to ensure that a round is chambered. When you pull the bolt back 1/2" or so, the bolt doesn't always seat fully when you let it go. A tap on the forward assist give you the peace of mind that the weapon is ready to go.