[pbz]

Using it as an alternative to documentation is a small part. First of all you get a confirmation that what you have up to that point is somewhat correct. If the dropdown doesn't show then something's wrong - sometimes that's ok and expected. You also get a type confirmation and actual completion as in type one or two characters and have the rest filled out for you.

[snprbob86]

It's just a different style of working, but I almost never type long symbols. I go to their definition site, yank them into a buffer, and paste them into place.

Or, I work with a REPL. So I write the code there and run it before putting it into my code base, so I know it's correct.