Interesting enough I had a alpha reader who checked out a fanfiction I did. He went on kind of a rant about how it was pointless and was for people who couldn't come up with thier own ideas and asked me several times what was the point?

I'll be the first to say most fanfiction sucks (including mine). I'm also willing to agree most fanfiction is smut (yep guilty)
But I've found when I need a break from what I consider 'real' writing...I write fanfiction so I don't get out of the habit of writing (even if its bad writing).
Also being able to write smut is incredibly useful for romance love scenes and heck non-fanfiction characters deserved to get screwed like everyone else.
I think one of the things I love most about fanfiction is trying to come up with a plot, even if its just two characters screwing theres GOT to be a plot by God!
So in the beginning, you try to draw interest (and with fan fiction the numbers break everything down on most sites) if traffic doesnt get past the first chapter you haven't got the hook right.
Then coming up with things, however rushed, to move the story to the end. Obviously if the numbers stay the same beginning to end you hit it.
If not, well I don't think writers get judged on fanfiction.
The practice is still the same and I feel like fanfiction is great to use to develop writing skills.
So don't dismiss it. Indulge in it for fun while you take a break from 'real' writing sometimes it's the thing you need to do to break down those pesky blocks that inevitably come up