You don't really explain a great deal about who this "I" person is. Are you a developer already? All answers are relative.
Assuming you're a n00b -
1) You'll gain the benefit of being able to write your own applications. This is something I, as someone largely dissatisfied with the majority of the general-purpose output of most commercial developers, find immeasurably useful. You, for example, might install an adware-laden tweak app to change your system settings after a fresh reinstall of Windows. You might need to install two, as one doesn't offer all the options you want. I spent an hour coding my own. I win.
2) ...lots. I can't imagine any 3D programmers using it as their primary choice (although D3D functionality is available), but it serves most purposes nicely when it comes to producing GUI and command-line applications for both Windows and Mobile (that is, WinCE, etc) platforms.
3) I don't so much recommend, more just prefer Visual Basic. It's the simplest language there is, it's the quickest to write apps in, and its object-oriented design fills me with inner joy. Having dabbled in other languages, I've not seen anything more pleasingly obedient than VB. But then, I don't write any low-level code or deal wth anything that needs break-neck performance, so my perception of it isn't universal.