Why do we use that phrase? Do we usually go around sneezing at stuff, so we need to acknowledge when we shouldn’t sneeze at something? I’ve never intentionally sneezed at anything, I don’t think. That’s not really like a useful form of ammo- you can’t control it that well. Unless you have that thing where you’re triggered to sneeze every time sunlight suddenly hits your eyes. It’s a thing, look it up. 

Anyway, I guess the phrase just means «Don’t overlook something.» There are plenty of things you shouldn’t overlook. This is a good thing to do, generally. Sometimes it can feel easy to write certain things off the map just because they don’t seem like things you’d be into. But that doesn’t mean you won’t end up liking them. For example, I went my whole life assuming egg salad was icky and gross. Then I tasted it one day and I realized I had been missing out for years.