Well, supposedly would help to tether a bit more...
Not only would it help tethering, but it helps with network congestion. Whether you have the data maximizer on or off, the more people that use it will lead to less network congestion and allow TMobile/Metro to utilize the bandwidth in a more profitable manner. It's beneficial to all customers and to Metro/Tmo.
For my 3 unlimited plan phones, I am leaving it on at the moment. Neither myself or the other 2 users watch enough video on the phone to have a problem with a 720p to 480p downgrade. This is very useful for those that tether a lot, the extra hotspot is an obvious plus as well.
All my music streaming is done through subsonic which allows me to play all my music from my desktop in great quality. I don't see Metro/Tmo ever allowing that to go through their service for free, and that is fine by me. It's one of the main reasons I'm on unlimited. If any of you have a large music collection at home and you dont want to deal with the various programs or clouds that compress or playback your music at different bitrates or a different format altogether, I recommend Subsonic. I pay $12 a year. It gives you full control over the your own server and allows you to add users/accounts to your setup. I have various friends who have full read capabilities to the multiple TBs of music. If you have a good, portable audio setup, enjoy the streaming FLAC that I was not able to see offered by anyone else at this price point.
All in all, I am happy that Metro is rolling out the same offers and innovations as Tmo, it makes Metro even more appealing. I would like to see how Metro's customer base has changed since the merger. At the very least, their operations have become more lean and efficient so if they continued with the same revenue, their profits have increased. I wish I would have invested into the company at the time of the merger.