Most of the answers so far have involved some sort of debugging code. Another use of __LINE__ (and possibly __FILE__) is to enable a macro to generate a unique identifier each time it's called. This implementation of coroutines in C uses these macros to generate labels for a case statement, so it can jump to the last line you called yield from.

Why would you use the __LINE__ macro in C++
I was once told that you should never re-draw a frame if the game logic has not changed since the last draw. 

Assuming game logic is updated once every tick, and assuming a game runs at 40 FPS @ 20 ticks/second, does that mean that every two consecutive frames will be exactly the same? If so, is there any visual difference between a game running at 40 FPS @ 20 ticks/second versus a game running at 20 FPS @ 20 ticks/second?

Perhaps I don't understand game loops that well, but it seems to me that ticks/second is a limiting factor of FPS.
