Increasing/Variable Startup and Shutdown?

So I still love my MBA (early '14). I've kept my Macbook focused on being a writing/music machine (only really use it for browsing, Pages, Garageband, have about a dozen pics in iPhoto... Aside from the pics and music files, nothing is on this computer that wasn't available from day one, no apps except for GarageBand).

From day one I noticed that occasionally the computer would boot up (from dead, I never hibernate or sleep it) without showing the Apple logo and bar (and sometimes it would show). Similarly, with shut-down I noticed that sometimes it was near immediate, sometimes it would spin for a while. I couldn't identify what variable affected this.

I'm a couple months into ownership now, and I'm noticing that while shutdown is still (mostly) immediate, I almost never get the 'boot without Apple logo/bar' thing going on any more. My startup folder is empty.

Is there a reason for this, anything else I should check? I know it's not really a 'problem,' I don't even think it takes a noticeable increase in time to boot. But... This bugs me.