How many forms could be cut?

[Mr Baggins]

None of them.

Not even the bad ones, since the bad ones help give historical context for how different parties involved throughout various DB media have viewed and pushed for them – cynically or otherwise. Dragon Ball as a whole offers a good bit of perspective on when transformations actually work for a shonen battle franchise like this and when they don't.

As for what makes them worthwhile, that's almost exclusively dictated by whether Toriyama was involved. Toriyama's transformations, typically when introduced for the first time, serve the story in a major way. They're milestones for progression, with clearly defined roles. Even the original manga's "failed" transformations demonstrated the growth of other characters while emphasizing important themes; I can write essays on the myriad ways that Super Saiyan 3 contributed to the narrative of the Buu arc, for example. And this is generally regardless of whether they were created at the behest of other big-wigs.

Of course, everything has its rare exceptions. Beast Gohan and Orange Piccolo are fairly interesting concepts with fun designs, but despite being designed by Toriyama, they marked an unavoidable point in Super (ignoring the anime) where the transformation wheels were spinning right off the cart and had nothing substantive to offer beyond memberberries and throwbacks. On the other hand, and conversely, Shintani's own "full power" Broly form did an impeccable job highlighting his increasingly unstable state of mind in DBS Broly.

Are there things I'd have done differently? Absolutely. But sometimes, it's more illuminating to take the bad with the good.

[BernardoCairo]

I really like them all to be honest. But Blue, Super Saiyajin 3 and Super Saiyajin 4 strike me as the most disposable ones (from Goku at least). I still think each of them is fun in its own way though.