If your objective is to build strength and bat speed I am sure it has merits. However, if your objective is to develop and maintain superior mechanics I would think that changing bats is ill advised. You change the bat, you change the swing. I find it interesting how many players at the lower levels have 2 - 4 different bats in their bag depending on the speed of the pitcher or how they feel that day. If you cannot hit well with 1 bat what makes you think you can hit well with 3?
I often thought the same thing. Nearly every girl on our team has multiple bats in their bag including my DD. Currently DD carries 3. 1 is the composite bat that she uses in games. 1 is an Anderson that she used a couple of years ago that we keep just to use in the cages (dimple balls). It is 1 ounce lighter than her composite, but in reviewing Eric's bat weight database probably isn't lighter at all. Then she also carries her very first bat which I now use to hit grounders to the team before games.
Another girl on our team carries 1 1/2 bats Her favorite composite broke during a fall ball game last year and she continues to carry the barrel portion of it as a souvenir.