The first is leveling out the tempo of my blog posts and how they show up in other social media streams. I often find myself neglecting my blog for long periods of time but then having these frantic (often late-nite) flurries of activity with all kinds of blog goodness to share. The problem is that this shows up as a flood of activity on my blog and in my Twitter stream and on my Facebook profile. Too much of a good thing all at once is no longer a good thing. Better to spread the goodness out over time. So, I use scheduled posting to write lots of posts at the same time but have them show up on my blog (and in social media) over a longer period of time.
The second benefit is time-shifting. For example, I often find when I have time to blog about an upcoming event (say, a conference at MITRE) is not the same as the best time for this to be showing up in my blog. Again, because my blog posts feed into social networks (like my LinkedIn profile), posting at 11pm may be when I have time for posting but I'd prefer it get visibility during the workday... or in a couple of days.
The third benefit is automation of posts that show up in my blog and in social media. This can be abused but, done carefully, serves a purpose. A use case for this is that if I am doing some recruiting at work I want to show up in my Twitter and LinkedIn streams on a fairly regular basis for some period of time that I have this opening but I don't want to have to remember or take time every day to post about this job. So, I create a number of micro-sized blog posts, schedule them over the coming days or weeks, and this way they trickle into those social media streams without any further work on my part.
If you use Blogger and want to learn about scheduled postings, this is described in the Google Blogger help pages at http://goo.gl/bMx0d.