No, it will not have any affect, neither to space usage nor to performance.

So why don't we use VARCHAR2(4000) all the time? Because the declared size of a varchar2 column is a kind of constraint, we set the maximum length of the string that can ever be inserted in it. It is the same as specifying/not specifying NOT NULL constraint or any other constraint for that mater. We simply set a rule and let the database enforce it.