In my case, it's not at all for the network effect, since these days they have too much content and anyway favor "premium" posts in terms of visibility...so for me it's more about the following:

* I don't need to create my own blog. I know, it takes a 5 minutes, have done it many many times before...just to kill it some time after because seeing it so empty was too sad. With Medium you publish whenever you want, and because it's not really "your blog", it doesn't feel as sad if you don't publish anything for months and months.

* it's super simple to paste images, code snippets and videos. I can just focus on writing and I know it will "look good" in the end. Sounds stupid, but it's true.

* I don't have to worry about spam comments, t&c, privacy policy (if I want to have analytics, which Medium has) etc...it's all on them

So yes, for a non-prolific writer, I think it works well. It's a pity they no longer allow custom domains though (which they had in the past), and at times it's toooo limited (eg: no nested bulleted/numbered lists...which I usually used a lot), but still good enough.

I'd probably switch to my own blog if were to publish stuff regularly and wanted to have my own "brand"/style/design.