Sometimes I need to use up multiple topics to fill in the daily word quota. Not only that, but there has been occasions when I had all those topics in my mind and wanted to get them out as fast as possible, or maybe they were just so current that it wouldn't have made any sense to write about them any later.
But other times there can be topics that just don't fit into a single post. Or at least they would make a rather long post. There might be enough to write about the topic for a few days, or even for a whole week (if you happen to go bananas).
For the former, there usually isn't room to write about more than couple of topics in a single post. But some topics just demand more than a few posts (even if you are not purposefully trying to keep at it). The later might happen more seldom, so in the end they pretty much even up each other.
And both of them can function as a source to yet another meta post about writing.