What is the use of #if in C#?

#if has lost so much compared to its ancestors -- c or C++. nowadays I use #if for only two scenarios

1) use it to enable code for debug or not debug

#if DEBUG
    // code inside this block will run in debug mode.
#endif

2) use it to quickly turn off code

#if false
     // all the code inside here are turned off..
#endi

#if (C# Reference) is a compiler directive. See the MSDN article for more info.