Tsk, tar me with all the brushes why don't you
I like a decent length of neat one spike guard for several reasons - getting a nice neat line sorted when I arrive at the crease settles the nerves nicely (though that goes straight out the window if I'm in lower down and the pitch is scraped to hell already), and I like it to be a decent length partly because alignment is important so I want to know where both feet are, and because I move in and out of the crease a lot to mess with bowlers' lengths, and it does tend to spoil the surprise if you have to remark your guard when you move out the crease!
On a related note, using running spikes to bat in last season was a revelation in my guard marking, so easy to get a nice line with a smaller spike.