If you want to pee, go pee.. There’s never a time on a train when you can’t stand up and do whatever you want. And that includes having a nice lunch in the dining car, which is what I’m going to go do now.
I really enjoyed a train trip my (then soon-to-be) wife and I took from Chicago to Dallas years ago, though certainly a plane ride would've been much faster. But for trips under, say, 250 miles or so, it looks like you won't loose anything but aggravation.
Maybe those proposed high-speed rail lines along the Trans-Texas Corridor are an even better idea than I thought.