I like to run actual coolant temps too. The factory gauge is buffered, so it reads points dead center between about 170-240 ish. By the time the gauge shoots up, it might be too late, if you're not a spot you can immediately pull over.
If I see my temps go above 220F and climbing, I'll either ease up a little, or switch off the A/C. Or at least the rear a/c since that's a bigger heat load in my case. But that's VERY rare. Really only happens when it's above 100F and after about 10 minutes of WOT climbing. If the engine coolant temp gets too hot, then the in-tank transmission cooler won't be adding much cooling anymore, and that's when the trans temps shoot up.
But more important, it'll give you early warning of a cooling system problem, before it becomes a big problem. Last summer, I had an issue with my engine temps hitting 240F before the T-stat would open. Never would have known it was starting to stick, if I couldn't see actual temps on the UltraGauge.