Comment by sarchertech

>If

A subordinating conjunction like if turns an independent clause into a dependent clause, so you don’t use a comma.

> And almost nobody writes sentences like "I love her and she loves me back" with a comma before "and".

In informal writing, people frequently leave out commas for everything but lists.

But it’s also very common to see it used “correctly”. In any kind of writing where someone would be expected to proofread what they wrote, I’d expect it.

The comma prevents readers initially grouping words incorrectly.

“I called John and Mary answered.”

Your brain will start to parse that as “I called John and Mary” before backtracking once you hit the last word.