When to "leave it out"
1. If you're inclined to write a nasty post. If you're just trying to be ironically funny, many times that type of humor is lost when it's in writing. But worse, if you truly mean to challenge another person's opinion in a confrontational way, don't.
2. If you're writing a word with a final S. It is correct more frequently to leave the apostrophe out than to put it in. An apostophe S ('s) means possession or contraction. It doesn't mean plural and despite what seems to be becoming prevailing usage, it should not be used as a warning that an S is coming.
3. If it's time to take potted plants in for the winter and you just can't figure out what all those little black dots are, and Raid hasn't helped.
4. If you're making chili and the recipe seems to call for an unusually large amount of chili powder and hot sauce. You can always add more later.