Useful or not - it depends on the situation, that is, if the team's results are terrible, or at least do not suit the management and the team itself, then yes, you need to change the coach and it will be useful. But in this situation, would it be useful? I think Bayern has problems, but not of such a large scale, they can be solved by the current coach
Considering the fact that Thomas Tuchel has quite a bit of experience and has also done a decent job with bigger teams like Chelsea, I think that he is going to be the right fit for Bayern Munich. The problem for Bayern Munich, I believe, is not the coach of the team, but rather the fact that they have lost one of their best strikers, Lewandowski, to Barcelona during this past transfer window. As opposed to changing the coach, I believe that the team should try to find a new striker to join them instead of changing the coach.
Regards
Duke
Losing Lewandowski is not the main factor in Bayern Munich's decline, because there are other players who can score goals for Munich. One of the factors behind Bayern Munich's declining performance was because the tactics used did not go according to plan, players seemed to lose connection when they were on the pitch.
If Munich wants to find a new coach, Tuchel can be an option, because he has proven to be able to give prestigious trophies to the team he has handled before. But Munich officials have to give at least a few more games to Nagelsmann, if he is not able to improve the quality of Munich's game, then a change of coach can be done immediately.