The "traditional" party movement scheme doesn't cater for multiple parties - if you have not individually selected a "partial" party, then any movement command gets applied to the whole party in whatever it's current formation is. So this is no good either.
I can't see why it's more complicated with a traditionnal scheme. You still have to select/create a partial party with the chain and formations doesn't exist at all.
Group / Ungroup / Locked characters per players / Group formations... This is easy, fluent and friendly user in many games that don't use the chain mechanic. (the end of this sentence is obvious... DoS 1/2 are the only games on earth from the beginning of the video game history using this system... a system which at best players are "ok" with).
I can't see any advantages related to the chain here. But I'll be glad to understand. Maybe you could help me with an exemple ?