alias parameters, what for?

[XavierAP]

What are the benefits of alias parameters, compared to specifying 
the template parameters fully?
https://dlang.org/spec/template.html#aliasparameters

In most examples, at places in Phobos, and in Andrei's and Ali’s 
books, alias parameters are used for functions (in the general 
sense). Why this instead of specifying and typing the parameter 
functions or delegates?

This brings another question, why is it so widespread in Phobos 
etc. to template these function parameters instead of declaring 
them as run-time parameters? Is this really always considered 
beneficial, why?

For one it looks like it saves a lot of typing and makes the 
whole declaration more readable (not to mention possible 
attribute soups); but the type-checking code just moves to 
additional template constraints.

And finally what’s the advantage of alias parameters in general, 
besides function/delegates? But I don’t see other uses in 
practice, although they’re possible.