Though they preach it like crazy in class. In reality, it ain't worth it. Most of them you'll find contain a mixture of fabrics, so it ain't going to be very helpful, even if you can identify with certainty.
You can almost always clean with fine fabric pre-spray (low Ph, not heavy on solvents etc.) and a "Wool Safe" rinse.
That will be good for most fabrics.
If in doubt (and always a good idea) test on the zippered back side of the cushion for adverse effects.
The white cottons, velvets, chenille's, chintzes, rayons; etc will need to be cleaned differently (different cleaning agents or techniques.) However, the majority of fabrics will do fine.
If you need to use much stronger products, usually it means that they waited too long and chances are the cleaning results will be somewhat limited. That is the time when the pen comes out and you better document the pre-existing conditions and set their expectations right.
Unless, of course, you collect upholstered furniture

.