How do you use your cosmetics before and after opening?

I think it is fine to use cosmetics within the stated expiration date as long as they remain unopened.

I try to use products within the indicated expiration date if there is any left after opening, but I've noticed many people strictly adhere to specific time limits, such as 6 months or 1 year. They throw things away regardless of the expiration date, even if there is some left. Recently, I threw away a toner even though it still had plenty of time left because my skin broke out. That made me wonder if I really should stick to the expiration date after opening, regardless of the actual date.

How do you use your cosmetics until they expire?