Using a Charged Tm

How many Machamps w/ good moves do you already have? I'd personally save them for Mewtwo, as after wasting 8 charged tms trying to get a dragonite to have outrage (to no avail), I can only imagine the nightmare it's going to be trying to tm Mewtwo.

Well do the math. How many more machamps do you think you'll find in the game vs. Mewtwos? You can almost solo a machamp at a t3 raid. Mewtwo is going to be more rare.

So in that scenario the answer is clear.

However, it's entirely up to you. If you personally feel Machamp is more desirable to you, for any reason, then do whatever you want. There's no law prohibiting you from using a TM any way you want.

Good answers here so far. I'll add that if you don't have a good Machamp, using a Charged TM will give you a highly usable Fighting move whatever the outcome. Yes, Close Combat is less efficient than Dynamic Punch, but it's still great at what it does. So it's not like you'll be on an endless revolving door of moves. One and done.