I'm surprised, particularly since I'm pretty sure the problems are rated against the players at the same time as the players are rated against the problems (which is how the problems get their ratings). If the practice you describe were widespread I think we could expect to see some rating inflation on both users and the problems as a result. I can't imagine why it would be offered either.
Why reset your Tactics Trainer rating & history?

It's not so much that you do, or I do, but if others do there's an impact to the integrity of the rating system as a whole for those of us who want to use it as a benchmark of our progress as opposed to a badge of our prowess.

there is at least one player on chess.com whose rating is in the top 100, whose tactics trainer rating was allegedly below 1600 .... something to think on there - - - until he deleted his tactics rating in order to conceal it from others. just something to ponder, why would his ratings be so radically different, unless......

Some of the "very best" players on this site have laughable live ratings, honestly, beginner stats. What they suddenly improve like 1000-1300 points when the pressure is off? Give me a break! It's completely obvious what's occurring.
Tournament ratings are used to develop a placement of player skills and strengths. It would not be interesting for a Master to always play against beginners. And beginners would lose interest always playing against stronger players. Certainly, simul events are interest stimulating. Player progress can be statistically documented by the rating systems. Bottom line is to enjoy the game and bring others into playing chess instead of running the streets or hanging out.
I never knew this feature existed till I took a look at Trainer Settings for the first time in quite a while..
So if your rating is 950 and you want a short-cut back to 1200, you might do this?
Is there a more legitimate purpose for this that I'm failing to imagine?
Cheers