Why router to create tunnel in the form of create the interface?
For example,
R1 (config) # interface tunnel 1
R1 (config - if) # tunnel source 100.0.0.2
R1 (config - if) # tunnel destination 100.0.0.1

Why not create a tunnel directly, rather than the abstract into the form of the interface, what reason and benefits?

For example, I think so configuration
R1 (config) # tunnel 1
R1 (config - if) # tunnel source 100.0.0.2
R1 (config - if) # tunnel destination 100.0.0.1
Finally also not to generate an interface, why not?