That depends on if you're blogging for the sake of "creative expression" to show an underlying theme, be artsy or your own unique perspective on things, or if you want to be topical by showing how much you know about a particular subject in which case your blog would need an overall topic because it would be high-brow and in-depth. Is your blog going to show what's unique to you as a person or what's informative about a particular topic using concrete facts and objective or technical knowledge? Or maybe your blog will be about current affairs so you'll need to write a huge amount of content in a short amount of time on a continuous and periodic basis?
Those high-brow blogs tend to only apply to a small audience. Most people aren't interested in the more high-brow topical things, like economics, playing a musical instrument or gardening.
Also consider if your blog is a light read or a heavy read. The Economist or MIT Technology Review is not the type of magazine or blog I'd read on public transport like a bus. But I sure could with those "viral clickbait blogs" like Buzzfeed, Huffington Post, Indy100 and Upworthy because they are low-brow.