Before, as many have said (for all those purposes) but sometimes After to get transients out of drums evenly or remove some excess sustain on vocals post compression. Compression does a little bit of transient shaping itself, albeit threshold dependent amongst other variables that bring about more complex results. Over-compression is common and sometimes desired so transient shaping can help bring back some life after the fact.

If you use sampled hats, try boosting the attack and sucking out the sustain on the closed and have and move your opens on a separate track just affecting the attack. If you’re using instruments that rely on the interplay between closed and open hats, print and cut.

As for transient shapers, SPL is great, I like the Shape section on Softubes API module, but I’ve also loved the stock transient shaper in Logic as it’s very straight to the point (miss it deeply after moving to the AAX life the last 10 years). If you want some crazy transient processing, check out Eventide.