Questions about example sentences with, and the definition and usage of "Needed"

A: "The professor will give a long lesson on English. Be sure to take adequate notes as needed"

"The food on the table is for everyone. There are also napkins for you to use as needed"

A: Personally:

I use "as needed" in situations where I *feel* something should/must be done.

I tend to use "as necessary" where may be external factors in play such that I have to do something.

In most cases no one will care which one you use.

A: same meaning, one is imagining the fact whether you will need "it" or not, and the other assumes you will, but proposes the scenario as a matter of 'time", when you will need it. both imply a possible future need for the thing... on this camping trip, take my number if needed. maybe we can pick you up.

take my number, when needed, call us and tell us where you are so we can pick you up.