Jeebus, I don't know what I'd do if I couldn't split lanes. It does save time on the commute, but the biggest advantage, IMHO, is the clear space that opens up ahead of a rider when leaving a red light. It's very nice to have a couple hundred yards ahead that's mostly clear of traffic, especially on the ride home. Lotsa cranky people during the afternoon/evening drive.
I've had quite a few drivers lean out their windows and ask me why I do such a stupid thing, and once I explain the clear spot theory to them, they mostly nod and agree. Mostly. Some just get really pissed that I'll be home quite a bit sooner than they will.