Significance of a .inl file in C++

Question

What are the advantages of having declarations in a .inl file? When would I need to use the same?

Answer 1

Since nobody else has mentioned it:

The use of .inl files to store your inline functions can be useful for speeding up compiles.

If you only include the declarations (.h) where you need declarations, and only include inline implementations (.inl) where you need them ( i.e. probably only in .cpp and other .inl files, not .h's ), it can have a beneficial effect on your header dependencies.

This can be a significant win on larger projects with many interacting classes.