As I see it, there are two primary functions for "tweener" discs, which is what you seem to be asking about, and which many people use discs like the TH for.
The first is as a gap filler. The farther you throw, the more important gap filling becomes. You if you only throw 350, and there is only 20 feet between your average TB shot and your average D shot, then gap filling is less important than it is for someone who has a 50 foot or more gap between those two discs. Even then, some people prefer to power up or power down on discs they already know and have than try to bring in a tweener. That's highly individual, as well as shot situational. Only you know if you want or need a tweener disc for the gap filling function.
The second function, which I don't see discussed often, is the "erring on the side of caution" function. That is, sometimes you have a TB shot, but due to circumstances (OB or other hazards for example), you may want to err on the side of a faster and/or slightly longer shot. That's a situation where even if you don't throw the TH much farther, it makes sense to bag and throw one, because on average it will be just that little bit farther. And in a game where one or two throws frequently separate you from the next place, we need every strategic advantage we can get. Likewise, you can use the TH for shots where you want to err on the side of slightly shorter and slower instead of throwing the D.
For either of those function, the TH is a good choice of a tweener between the TB and D.
