As I didn't know it, CTRL+MAJ+2 command opens a contextual popin listing your file's methods.

While coding, it can be a mess quickly in this list. This is where mark saves your life.

Xcode gives you a pragma mark metatag you can use in two ways:

First:

#pragma mark -

adds a separator (as <hr/> html tag) in the contextual list.

Second:

#pragma mark Your great not to long description

gathers methods in a group named Your great not to long description.

This two uses of Pragma mark allow you to visualy organise your code.