Two quick cents. I don't see alt policy (none/one/four/whatever you can play) as being the issue that makes or breaks a game.
Some of the arguments say less players means more positions of powers for players, but I support what @Arkandel said earlier, positions of power shouldn't make or break a character and their story. Someone else mentioned interpersonal relationships are a prime draw to Mu*'ing over say TT or even OTT campaigns that are episode to episode.
Ultimately I think it comes down to the player and their investment into their storyline that fits within theme/meta that makes or breaks interest in a game for that player. A couple months ago I asked about meta and such and everyone seemed to favor staff having to run things, I'm still not sure if this is the way to go, staff having to control meta to the point of giving folks something to do.
This may be from decades of being a daytime player only. The majority of staff only do things in evenings, just the way it is ... all the haters that come to my places and complain about daytime activity, you've no idea how much worse people that play during my connect times have it with the feeling left out part.
I've always just made my own story, folks can call it sandboxing, but I can't get into meta which is 90%++ only in evenings (low estimate to be honest because I'm trying to be nice). I always find it that interest should be player driven.
If they want 4 alts in less active relationship circles (@faraday mentioned 4 meaningful relationships per PC regardless of alt policy, but some may only RP with 1-2 others only), only want to focus on social drama and their IC relationship, and it keeps them playing with those others, let them have at it. If someone else only wants one alt and interacts with the entire grid and drives their own stories separate from staff meta, more power to them.
I view Mu* more as an environment to encourage creativity, to give players some place to play, to hopefully be safe for them to come and simply enjoy themselves. If that commitment is once a month and they want an adventure on their one day a month, I think the opportunity should exist. If they are daily and socialize only, that opportunity should be there (dependent on activity of other players).
I see a lot of focus always pointed at staff, staff should have alt policy, the should police all player activity. I'm more aimed at the player, if a player can't go out and make their own fun, or find the players that do that, its more on the player, regardless of who has one alt and the ones who have 12 alts.
Sorry, I took the thread and borrowed the soapbox for another topic, but it seems fitting. Arguing about alts, when, if maintaining interest and vestment in a game is what the discussion is about, seems off the heart of the discussion.
Edit to add instead of posting my own reply:
The common topic 'There is nothing to do here', I place more on player than staff. Staff should have opportunities for things to happen, I think it gets players together and that should be the focus of meta, getting folks to mingle more, creating some new potential hooks for players storlyines, introducing ideas of what can be done on the game to help inspire their own plots and stories.. I think things to do anywhere, having something to do, is on the player. I think restrictive PrP policy is more damaging to activity than alt policies and blaim staff for not allowing player creativity to flourish.