Fish under the weight rating of the tippet can break the tippet. So even with 15# or 20# tippet, a 6 or 8 pound redfish can break those. Ask me how I know! I’ve lived it. Gripping the fly line too tight to the rod at the take is a good way to break a tippet.
Fish over the weight rating of the tippet can be brought to hand.
This black drum was over 30#, bottomed out my 30# boga, and came on Seaguar grand max tippet that had an 18# rating. I wouldn’t cast to a big drum like this one again. It took too long to get in on my 8/9 weight Short Stix. I like fish that can be brought to hand in a relatively short amount of time.
I think fly fishing by some of the definitions only allows tippet up to 20#. Maybe it is the IGFA and that’s if you want to submit a catch for their record book.
That’s another whole subject and not without acrimony, people catching big fish on super light tippets to get a record. Some hate the idea of lightly and long playing a fish to avoid breaking a light tippet to the point of complete exhaustion for the fish. The idea is that the fish won’t recover from the event even if released. But there are those that pursue tippet class records.
12-20 pound tippet seems pretty appropriate and good in many of the Texas inshore settings. Snook, from what I’ve read, need a 30# bite tippet for their super sharp gill rakers. Really sharp toothed fish need some type of bite tippet. Maybe there’s a situation that would call for lighter tippets in the Texas Saltwater, I just don’t know. I don’t see any reason to go over 20# unless maybe with some offshore species.