That's fine and all, but it's pretty much the biggest trap in the Core feats, and that's saying a lot. You only get a handful of feats in your entire 20-level progression, and Toughness gives less HP than the average HD roll of anything but a Wizard. And again, I'd still call it the biggest Core trap feat even when compared to things like Craft Staff, most of the pre-reqs. for Whirlwind Attack, &c. The only worse one I can think of off the top of my head would be taking Eschew Materials when your DM isn't anal enough to make you keep track of spell components.
Of course, as before, it's your choice. The thing going for Rolepgeek and myself (and Avis, considering that this is Core-monk we're talking about) is that we're playing decidedly suboptimal classes to begin with, and will naturally fall behind because even poorly optimized T1/T2 classes will still scale very hard. Take my example, a Barb/Fighter. Depending on whether I optimize, my mid-late game levels will be spent with be either being useless because anything I'm good at can be done more effectively by other people, or supremely good at one thing (in this case, jumping on peoples' faces and making them regret ever being born) and mostly useless at everything else.
That was actually part of the motivation behind that kobold Batman character I made, designing an optimized sub-optimal build (Rogue/Swashbuckler specializing in rapiers, poisons, and thrown alchemical items? Lol) that would still scale pretty hard into lategame because it would have the versatility of a Wizard, if not the power.
The bottom line is that if you're playing a 'naturally' optimal class like a Wizard, Sorc., Druid, Cleric, Binder, &c., you're completely free to do whatever you want with your build, because it'll still end up being fairly strong. If you play a 'naturally' suboptimal class like a Paladin, Fighter, Rogue, Monk, or (gods save you) a Warrior, not optimizing means that you're going to spend a whole lot of time watching other people do what you're supposed to be good at even better than you can.
It says I still have to be, implying I had to be in the first place for that section to apply.
I can rules-lawyer just as good as you, Nerjin.
Except for the house rule section I suppose. I think I recall Mr. DM saying you can be a Chaotic Good palidin. In most cases you can't take a level in paladin without being LG.
It helps to read, I think. He's starting as a CG Bard and planning to later take levels in Paladin, which will require him to switch to LG, but he also will take a feat which allows him to continue as a Bard while being Lawful as well as using his cross-class levels to determine his Smite Evil and bardic music strength. After the DM specifically allowed non-Core feats.
Hell, there's practically an identical one which allows Swashbuckler and Rogue levels to count for each other for determining sneak attack damage and the strength of various Swashbuckler class features.
Wouldn't toughness pretty quickly become ineffective towards higher levels? Maybe for really squishy, low level characters, but later on you might regret not having a more persistently useful feat.
Very, very quickly. As above, it offers less HP than the average HD roll per level for any class but a Wizard/other d4 classes. So it's outscaled by one level (or a fraction of a level) for most classes (or a lucky d4 roll), or two levels for classes with d4 HD. Plus it's a
feat slot. Those are one of the most limited resources you have, and HP, even for a super-squishy super-low level character is a pittance compared to what you can get.