I fully believe that people who do it for a counterbalance think it feels better. Pretty convinced that the physics don't actually add up though.
The counter balance works for me. People who have used my bats in the nets and in games say they like it.When I move my bats on it is only tape so it can be removed. Only one person has done that so far.Try it, maybe it works for you.
The problem is that (as Kulli says) unless your pickup is very strange indeed you're still picking up and swinging the whole bat, including whatever additional weight you might have added to it. The extra grips/whatever else can only make the pickup heavier. It does give you a good point to moor your top hand against at the end of the handle, similar to a baseball bat, which is why it's most popular with taller players.