So in playing a ton of 3s, I've noticed that a lot of teams prefer to have 3 laners and no jungler. Why is this? It seems like, while it's hard, jungling confers A LOT of benefits.

A lot of people don't feel like doing the inevitable 2v1 lane because the other team inevitably won't have a jungler (unless it's a premade or mid-high elo ranked), which is understandable because that severely limits the champion choices they can do and play well.

Not to mention that the 3s jungle is brutal, unforgiving and scary. A lot of people go into the 3s jungle thinking it's like the 5s jungle and they get facerolled by the buff camps. So instead, people play a kill lane bot and have a solo top champion who does a sort of "half-jungle" - which, although inefficient, works fairly well in some circumstances.

My team runs one per lane and a jungler even in normals, and I play the solo bot most of the time. I'm fine with it and we all practice our roles, but it's understandable how casual players wouldn't think that jungling is worth the trouble.

There are very few junglers who can operate in TT. Almost all of them are manaless or someone who never has mana problems (e.g. Voli, Yi, Xin, Nunu)

Pretty obvious why.

The jungle on TT is as hard as the old jungle on SR but with less safety and not as much reward. Because of this there are few champions that can make use of it. That ones that can really do well there, nunu for example.

Because the Twisted jungle is slow, brutal and incredibly hard without blue. It also forces you onto the enemy side of the map, and if you're so much as glanced at by the enemy team it's a free kill in a lot of cases. The randomness of the buff camps is also a huge factor. Did you get wolves, green buff and the motley crew? Smooth sailing. Is your jungle 100% wraithes? Enjoy fighting raidboss black buff.

I don't play a lot of Twisted Treeline, but the last time I did I took Skarner top lane and semi-jungled. I would push the minion wave, then clear a jungle camp. As I got higher level and stronger, I'd push the minion wave, then kill 2 jungle camps. I found it gave me a real strong exp and gold advantage over my laning enemy. It felt less like jungler on summoner's rift, and more like how the mids try to take both wraith camps. I liked it, and it seemed effective.

Aside from the jungling difficulty and low reward, if you attempt to jungle in solo queue, most of the time your teammates will rage and complain all game (because they are bad at the game and cannot 1v2), and will fail to protect you or call MIAs out of spite. If you get ganked as a jungler in solo queue a single time and die pre-level 6, you have already lost the game. That kind of gamble is far too risky to make it remotely viable.

Right, the jungle is hard, but the benefit you got from having a jungler is SO large. An AD like Yorick (who has lots of poke and decent sustain) or Olaf (who scales pretty hard with levels on his E and has poke/sustain) can usually handle the 2v1 lanes, albeit with a slight CS disadvantage.

Do you guys disagree that jungling provides a huge advantage?

For those players who play normal 3v3, all the way up until level 30 it is a poor decision to have a jungle.

The reasons being that:

1) Before level 30 it is extremely rare for a player to have the proper runes and masteries to be able to deal with the Twisted Treeline mob camps effectively.
2) Before level 30 it is very rare to see a player play 1v2 effectively unless they are playing on a smurf.

For those players who play ranked 3v3 between the rating of (0 - 1300) it is rare to see a jungler as:

1) It is all in all hard to play correctly. And with little to no practice pre-level 30 it's very hard to pick up and can really only be learned if taught.
2) You have to have very good team coordination to time / plan jungle ganks while at the same time you must have a very talented bot lane who can deal with 1v2 OR deal with 1v1 and prepare for ganks.

Having a jungle definitely has huge benefits. Among those:
1) Higher levels on the team all around.
2) Higher creep score on the team all around.
3) Very strong ganking opportunities.
4) The spell 'smite'. (Every buff, every dragon, all yours)

The only cons that come with having a jungle is that one lane is often left to 2v1 (which can often actually be a pro (higher level higher creeps score than the 2 opponents))
And that you are down one summoner in a team fight. But hell, you probably have dragon buff.

Hope my answer helps!

In a practiced team, yes there is advantage.
But in Blind Pick, you are stuck picking your bottom lane *assuming* a 1v2 situation, which severely restricts your teamcomp (considering how few champions can reliably 1v2 when faced with a strong kill lane, and how few champions are strong junglers on TT).
Which ends up meaning your top lane often has to pick to complement the other 2 lanes, which usually means a worse 1v1 scenario.

And in Draft Pick? Whichever team picks their jungler first is at a HUGE disadvantage, because the enemy team can immediately decide whether to counter the bottom lane, or the jungler.