[julia-users] Difference between {T<:AbstractType} and just x::AbstractType

[Igor Demura]

What exactly the difference between:
function foo{T<:AbstractType}(x::T) = ...
and 
function foo(x::AbstractType) = ... ?
Is any difference at all? The "tips" section of the docs says the second is 
preferred. If they are the same, why first syntax? I can imagine that I can 
benefit if I have several parameters:
function bar{T<:AbstractType}(x::Concrete{T}, y::AnotherOf{T}, z::T) = ...