Never.
"Read my fanfic!" pretty much tells me what level a "writer" is at. It hurts to even use the term "writer" when it comes to fanfic creation.
The fanfic I see are:
1. I want to wank to the characters in X, so I'm going to write bad
**** about them!
2. I can't come up with a universe.. or characters.. but I think I can come up with a story if I steal someone else's universe/chars!
3. I wanted the episode/movie to go this way, so I'm going to write that!
4. I worship this so much, I need to write about it, so I can add myself as a character! I'm going to be so cool!
5. I'm going to combine 1 and 4!
Generally just about all of it is cringe worthy/sickening.
You just want to cry when you find they have been sending their "ideas" to the creator for some time... or even better when the fanfic writer says the creator should no longer be allowed to write about those characters because the fanfic writer's stuff is so much better.
If you are fresh to writing and cutting your teeth on fanfic as it allows you to work on just a part of writing, that is fine but you probably do not want to show your stuff to to many people and you most certainly want to get out of fanfic ASAP.
Honestly, I respect the
**** writers the most when it comes to fanfic.