Adding a new worksheet
Viewing tip: Press the 'Play' button, and then the 'Fullscreen' button on the right.
Should you add more worksheets?
Well, the obvious answer is - when the three given aren't enough - yes, add another one.
But - take my word of advice - don't add too many worksheets, because it will quickly become hard to handle. You might find yourself lost searching and scrolling to find your specific one.
How much is enough? I would say a dozen (twelve). A file with a worksheet for every month is decent.
I once was in a company where they had an Excel file in which they added a new worksheet every week. In one year it became into a 52 worksheets monster making it impossible to draw any yearly conclusions.
What should they have done instead? Write it all in one big table, or at least arrange it by months.
If you are a teacher, don't open a worksheet for every student, write them down in one big table.
As a rule of thumb - Try to write all your data in one big table inside one worksheet. This way you can use it with a pivot table. A pivot table (I made tutorial videos for this subject too) enables you to easily draw conclusions out of your data (including summations, averages etc.)