On occasion I omit

On occasion I omit commas. On occasion, I use them. (The more you know about English, the less you’re likely to think there are unbreakable “rules” for a lot of these things.) Bill Walsh

The dash helps to

The dash helps to indicate that the two thoughts are intimately related, and it’s less stodgy than a semicolon, which would have performed the same function (and who talks in semicolons?). Bill Walsh