How much to “automatically” do?

Question

I'm reading Code Complete 2, and I'm at the chapter where it says to (paraphrasing) "avoid programming through the interface." Why is it bad to program "through" the interface?

A more concrete example: if I have a method of a class that submits a funny picture, what's wrong with it logging me in also? Should I simply provide more "helper" methods that do it automatically?

Would it be preferred to break it up into:

• set_login(username, password)
• login()
• submit_picture(funny_picture)
• easy_submit(funny_picture) # where it will log in (if not already) and submit