There is a difference in (American) English.
Contractions are not stylistically acceptable in formal writing, but are acceptable in informal writings such as personal letters, newspaper articles, novels, etc.
They are also acceptable in most speech instances.
The contraction is also the common form in speech; if one uses the full form it is to add emphasis to the statement.
For example, if my wife says "You can't watch football today because you need to clean out the garage" I know that there is wiggle room.
If she says "You can not watch football" I know we are in for a dustup.
