Intellisense

Intellisense is basically auto-completion when you are typing.
This displays a short description of member, function, arguments etc next to the cursor and is a convenient way to access functions, parameters, enumerations etc.
Using intellisense speeds up development by reducing keyboard input.

Auto List Members

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Auto Quick Info

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Automatic Intellisense

Range("A2"). 

No Intellisense

There is no intellisense with the following code
This is because the Sheets collection can contain two different types of objects

Sheets(1). 

This is because ??

Worksheets(2)