There are over 4000 built-in functions in

*Mathematica*, not including those in add-on Packages.
In[340]:= Names["System`*"]//Length

Out[340]= 4131

Therefore it makes sense to see if there is a built-in function before we write one. Likewise, the large number of functions means that we often have a vague memory of a function we've used but can't put our finger on its name when we need it again. If I have some idea of the name of a function I've used, or want to see if there is an existing function and guess at part of its name, I use a wildcard in my current Notebook with the short form of Information (?). To find a function or survey related functions, this is faster than using the Doc Center.

Here I want to know the filepath of my current Notebook, which I cannot find in any

*Mathematica*menu item. Maybe there's a Notebook function to tell me. I scan down the results until I see NotebookFileName, which is the one I want. I also quickly click on a half-dozen or so functions to refresh my memory of them or explore new ones and read the short info displayed below the results.
Using Information this way is always fruitful for me since I efficiently learn about functions I didn't remember or didn't know. But if it fails to flush out the function I want, I go to the Doc Center and search there.