are there any advantages and/or drawbacks using it?
An advantage: less typing.
(I think that using var is not very readable)
I partially agree with this point.
It is less readable when you have var s = foo(); instead of string s = foo;. In other cases it can be more readable.
How about performance
At runtime there is no difference. The compiler converts it into the same intermediate code as if you had explicitly stated the type.
