"only" vs "[]"

[pascal111 via Digitalmars-d-learn]

The output of next code is the same to extent that we feel that 
there's no difference between "only" and "[]", so what "only" 
added here?:

'''D
[1,2,3].writeln;
only(1,2,3).writeln;
'''
output:

[1, 2, 3]
[1, 2, 3]