To be honest, I'd rather they only let the player be a member of one linkshell at a time.
It's a pain to try and start a linkshell when all your members are switching over to other ones, then the new people see it's a fairly barren linkshell and leave for another one, etc.
I had quite a few linkshell pearls, some of them for specific purposes:
1) Social/Event LS - - I joined when I was around level 30, and remained until I quit.
2) Dynamis LS
3) Beastmaster/Summoner LS - - I was recruited while I was soloing in the Boyahda Tree. We did Jug/avatar burn parties, OHAT/Carbuncle's Mittens runs (Which made me a lot of gil), BCNM/KSNM's, and took down a number of HNM's. Got my Kraken's Club from a BCNM doing all BST party.
4) Endgame LS - - I was recruited to do crowd control with my BST to help a new endgame LS get all of their magic casters some Rostrum Pumps. They had no Bards, and I already had CHR gear from my BST, so I leveled it. As BRD I got Sky and Sea with them. Eventually, the LS grew powerful enough to take on pretty much anything. If it weren't for them, I would have never gotten my Speed Belt + 4 million gil of other drops. We did Your-orb-your-loot for about 30 orbs, all day event, once a month. I did KSNM-for-hire with 3 BLM's and 1 RDM once a week and made a nice commission off of it. And loads of other stuff, I won't bore you with.
Honestly, I don't know what I'd do if I were forced to remain in one LS at a time. It would be a nightmare trying to get certain events done with all of that typing congestion.
Having more than one LS helps a player to keep his/her chat organized.
Character name: Undecided
Armoury: Desciple of Magic/Land/Hand
XBOX Live: TheJollyJokers