Question: I'm using the `VLOOKUP` function and I have this function `=VLOOKUP(B9,Products!A5:K29,11,FALSE)` 

It works but what do I need to add so the cell will display nothing if B9 is nothing? At the moment if B9 is nothing it displays "#N/A".

Answer: 
This folder is essential for all the programs that you have installed. To prevent the "[DLL hell](http://en.wikipedia.org/wiki/DLL_Hell)", Windows copies required DLLs for every single installed program here. This way, installed programs do not influence each other. It is very common for this folder to grow over 10 GB and beyond. 

Try uninstalling some unneeded programs, see if that helps. If you want to keep the folder small, reinstall your Windows and install as few additional programs as possible. But that maybe defies the purpose of having a personal computer at all.

So in short: it is a necessary evil to live with. It is a price we pay for compatibility.
Quoting from this [link](http://www.winvistaclub.com/f16.html):

> 
> There have been several blogs and even some “underground” tools that
>  tell you it’s ok to delete the WinSxS directory, and it’s certainly
>  true that after installation, you can remove it from the system and it
>  will appear that the system boots and runs fine. But as described
>  above, this is a very bad practice, as you’re removing the ability to
>  reliably service, all operating system components and the ability to
>  update or configure optional components on your system. Windows Vista
>  only supports the WinSxS directory on the physical drive in its
>  originally installed location. The risks far outweigh the gains
>  removing it or relocating it from the system, given the data described
>  above.
> 
> 
>