After doing some quick brainstorming on initiative, I couldn't stop thinking about the subject. It took me a while to understand why. As I've said before, I don't usually appreciate heavily detailed initiative rules - giving initiative based on the situation or in order of DEX is good enough for me.
Still, there is some ideas I like about “segment” initiative that are hard to find (or not as interesting) in simpler systems. The main one, as you may have guessed, is stopping a wizard in the middle of a terrible spell.
The trope is quite old and justifies a few other things I like. For example, you can have earth-shattering spells that do not make the fight one-sided, and that are very risky for the wizard himself (because he can be stopped mid-spell, and lose the spell - not to mention his life - in the process). Spells get to be amazing being too "unbalanced".
Most important, this forces characters (PCs or NPCs) to work together. For wizard PCs, spell-casting is no longer a solo game, but a tactical group effort, with the mighty fighters protecting the frail wizard to allow him to finish the spell. For wizard foes, the PCs must find creative ways to stop their spells - maybe throwing weapons (improvised or not) at him, or just getting out of the way.
|... and sometimes you just have to play dirty.|
This, in a nutshell, is why I want a detailed initiative system for my game, and what I'll try to do next.