Repack bearings?

Ok, so in a few days I am going to attack replacing my passengerside cv shaft. I know on my explorer it was recommended that I repack my bearings whenever they are removed. I know that the s10 has a complete hub/bearing that doesn't really get taken apart and dismatled. I was at my local generic brand named auto parts store and saw they have a tool which basically sandwiches on either side of the bearing then using the grease gun forces the new grease inside. I was wondering if this would be worth doing, or would I be wasting my time. I figured since I would have it all apart why not get it if it may help or extend the life of my bearings.
THanks

89 s10 4x4 4.3L

If the sealed bearings are low on grease they are usually bad.