Is it important to give files and folders descriptive names?

Is it important to give files and folders descriptive names?
Yes, as this gives you an easy means to identify what that folder or file may contain.

For example lets say you have a spreadsheet listing your income, and expenses over several years.

Naming it "Spacedonkey" won't give any clue as to what the file is about.

If however you named it something "Accounting 2000_Current" it tells you what the file contains.