[Vala] [Async] why use .begin ?

[JM <interflug1 gmx net>]

Hi all
A few days ago I edited the asynchronous stream reading example on the
vala site to use the new async syntax.
http://live.gnome.org/Vala/GIOSamples#head-a6170c01121b9fe5825f431de73573b084545741

After the release of vala-0.7.6 I realized that other examples of the
new syntax use '.begin()' to call the async function.
I compiled the example with and without the .begin keyword and found NO
DIFFERENCE in the generated C code. Both ways are working properly.

Is there a case where the difference will be more clear? 

Regards
Jörn