How do I know why I have a port?

[Jeremy Lavergne]

> Sometimes, I notice I have some port installed that I have no conscious interest in. I'm sure it's there because it's depended upon by some other port that I do care about (or recursively), but is there some way I can find out what that would be?
> 
> I see that "port info whatever" tells me what stuff "whatever" depends upon, but I want the inverse of that.

port info will include the info of:
port depends x

the reverse is:
port dependents x

you can also use this as a pseudo port:
port echo depof:x
port echo rdepof:x