This might seem like a silly question since they are one of the coolest, in my mind, units ever in any RTS, but do Krogoths really justify their exorbitant cost? I've found that they're best used to take out either a ton of low level units, weak armored units like aircraft when they finally get taken down because of their massive explosion, or as Commander Hunters.

Their no use at all for quicker games, but for longer ones, they are brilliant!

Best on metal maps.

They are the best defensive unit you can get, i like to hide them behind hills around my perimeter or patrol them.

They are also very good for assaulting well established bases..... some metal maps, it is almost impossible to crush the AI without a few Krogoth assaults.

Get heaps of advanced construction aircraft helping construction and they can build quite fast - if you have the metal!

My take is anyone who can build a Krogoth is outclassing their opponent to the extent that they should have already won the game.

That's your typical multiplayer game against human players. But its usually fun to extend games against AI - or you can even extend multiplayer game with a timer - get half an hour before combat is allowed, then Krogoths can be very useful

Yeah, I have only ever built Krogoth against AI and even there, it usually involved beating the crap out of the AI, and then letting it live while I built a Krogoth.

Do a metal map on hard with 9 AI allied against you.... you wont get to beat the crap out of all 10 early on that's for sure!
they will be wiping everything out you can throw at them soon enough. You can do nukes or intimidator creep or Krogoths.... i know which is more fun! :)

My skills aren't that sharp. No doubt 3 AI and hard, on metal map would probably kill me.

Nah.... defending on a metal map is easy.... its a metal map! So you can build defenses quick.
Defending against 9 on a map like green haven is actually much harder.

The thing with the metal map, the hard part is about taking down the enemy, because the AI are super resilient on metal. But their attacks are still somewhat weak, unless you have an AI mod in which case i would say your doomed!

I want to try using more Krogoths offensively in the future against the AI. So far I've had a hard time keeping their main blue antimatter cannon( think that's the right term) powered up. Seems like every time I get to level three structures I have to take time to use air raids to take out a Big Bertha or Intimidator so that by the time I can get a Krogoth built I don't have much space in my unit cap. Krogoths still take out most of the enemy's attackers all by themselves when I'm playing. Seems like the AI in TA cares more about constant pressure through wave attacks than being patient and building up something massive I'd really have trouble with. READ: I am using no AI mods.

Well no one can use massive attacks in unmodded TA because of the pathfinding. The only mass attack you can do is with air units.

As for the unit limit, well, once i have a sufficient advanced fighter screen, i pretty much demolish all my level 1 crap except for a few guardians, and eventually even they get blown up once i have Krogoth defenses. You should not be keeping anything level 1, not even level 1 construction vehicles and construction aircraft (well keep one of each for if you want to build more advanced factories)

...not really. Pathfinding has been updated already so you can do it in OTA.