Hi Eddie,
One thing to realize is that for the most part the way people will find you is through search engines. If the site is about pop culture and you write a post about golf it's not likely it would get ranked high enough that anyone would find it. Therefore it's not going to help widen your audience at all.
Plus it could be a turn off to your visitors who are looking for info about pop culture. Now if it's off topic a little but related and/or especially if it's something that your visitors would most likely be interested in, then it's probably OK.
But search engines LOVE consistency. If your domain name is about pop culture and the site is about pop culture and the posts are related to pop culture then you'll get ranked higher for your main keywords and related keywords.
Example I can pretty easily get ranked in the top 5 for all but the most competitive affiliate related KW. Even for
SEO and blogging KW I get pretty high, because it's related and I write a lot about those topics too.
If I wrote an article about golf it would be on page 2,385 in Google, therefore no one would ever see it.
Does that make sense?