Walking should be on the outermost perimeter. Insides is for all other things.
I agree, but . . .
Those who are new [...] do so inside.
. . . the fact that this is known to be the case causes issues.
It may just be where I live, but many new people don't to want to be marked as new; consequently, they try to mask inexperience by dancing in the outside lane with the experienced dancers. They soon discover that when their teachers told them that the walk is the most important thing in tango, and that it takes a lifetime to master, it wasn't a lie: They have a mediocre-to-bad walk that they cannot calibrate to the speed of the ronda, causing them to tailgate or block the line of dance; they soon get frustrated and falter; and they end up disrupting the entire outside lane.
When I started tango in 2013, this problem was sufficiently prevalent here that beginners were taught to stay in the outside lane because "people dancing on just one side of you is easier to handle than people dancing on both sides of you." I've since realized that was a sneaky attempt to scare beginners out of all the lanes that weren't the outside one, and not really the way things should be.
Inside depends on the size of milongas. Some have two lanes with enough space inside the second lane for third chaotic lane or dancers that want to moves that take up space.
Here we most often get two real, (mostly) circulating lanes around a center big enough for maybe two or three couples to stay in place. Some large events have three full lanes around the center. A couple of very small places have two lanes and no meaningful center. The tricky bit is that the same people move from venue to venue and bring things that work at their "home" or preferred milonga to others where those things don't work.
I only seen a very few times organizer enforce the lane and ask those disrupting the flow to dance inside.
A couple of local organizers take time to mention the rules, but they don't enforce
or follow them. They talk the talk but don't walk the walk.
I had an out-of-town friend here over the weekend and ended up doing a private "mini-marathon" with her. Lots of dancing, but it's getting warm and humid here, so lots of pauses to cool off, too. I noticed a few things that consistently caused traffic problems:
Dancers who start with their feet. They step and then displace their body; they don't displace and bring their feet along because they're attached. So, an unweighted foot gets stuck out way too far in advance of the movement while they almost lean backward over the weighted one. Looks like
this. Uses up way too much space and causes them to advance jerkily and not smoothly.
Dancers who look at their feet. Meaning they're not looking where they're going. I saw two
teachers doing this . . . Why?
Dancers who never abandoned the back step. I could kiss Julio Alvarez (current partner of Silvina Tse) for what he said at a workshop just over a week ago: "Traditionally this starts with a back step. But this is 2024, so we don't to that any more." And he didn't back step at the milonga. He walked the walk.
Dancers who offset their partner. Leaders and followers are equally to blame. Their partner is off to their right, so the leader is mostly visible on the open side and the follower is mostly visible on the "closed" side. The result is a couple that's 50%+ wider than it needs to be, which is a horror film in turns because it sweeps out this huge circle, half of it against the line of dance.
Dancers who turn in place. The leader has never learned to add a forward component to a turn, advancing the couple as they turn around each other. Yes, cadenas are hard, but simple walking, parallel-system turns moving forward were the first turns I was taught in tango. Are these not still taught?!?! The mini-version of this is the linear rather that circular ocho cortado – another thing Julio said we don't do in 2024, thank goodness.
You'd think "keep your partner in front of you, look ahead, move forward with all steps, advance your couple's center of mass and not just your feet" would be common sense, but it appears that it is not.
Obviously, I'm speaking of crowded milongas here. Do whatever you like at empty ones. But of course that's part of the problem when dancers from places with mostly empty milongas come to crowded ones. As noted above, people move from venue to venue and bring things that work at their "home" milonga with them. They don't adapt.
But what if she is wearing flats!! Leading a good boleo can solve many problems 
. Nowadays it seems 'reserved' for those who think they're 'better'.
