You want to keep paint from decorating to touch up dings, etc. When you get out the bucket after long term storage it's such a pain to get all the settled pigment off the bottom of the can. If you don't the color may not match and the mixing can seemingly take forever.
THE SOLUTION? STORE THE CAN UPSIDE DOWN.
All the pigment is now on "top" when you open the can, mixing is a two minute job, and ALL the pigment is re-dispersed.
If you have a custom color that usually has the color label on the can lid, brush a sample of the color on the side of the can or label the room it is to be used in.