What Is A Good Sign It’s Time To Clean The Fridge?

I am the type of person that checks the expiration or "sell by" date on everything. Still when you have things at home, there isn't a set date to throw it out. I hate letting food go to waste. Especially when it was a dogie bag from a place you really like eating. Is there a good rule to fallow when it comes to homemade or carryout food and how long it stays good?

Lately I have been doing the smell test, and it is one good way to cut down on eating because I am never hungry after.

How do you know when to throw out food?