But still what is the use case?

I mean if i wrote code which is functioning why would i replace it with some one elses code?

Taking in raw code even (especially from) OSS repo's is a huge huge can of worms.

Say you are developing a product if you use an OSS library which is distributed as is you can bundle it with your product under most licenses unless you modify it without having worry about anything.

If you copy paste code form that library into your own code base well than what is it? a copyright violation? derivative work? I can easily bundle OpenSSL with their Apache license and just make a remark about it some where during the installation, i don't have to distribute my software or source code under that license or under any other OSS license.

But if i take the raw source code say their ASN.1 parser and implement it in my own program? what now? I'm not an IP lawyer but I'm pretty sure this either violates the license outright or my software now just became some derivative work which means the terms (or some of them) of the original license now apply.

Even if my software was meant to be OSS it's still an issue maybe i don't want to use Apache or BSD maybe it want GPLv2 or V3 or my own license or what ever.

The other issue that stands out to me is that I already wrote functioning code, it works, it's mine, i know it i understand it i can maintain it, why should i on-board someone elses code that i won't know, won't understand, wont be able to maintain as easily? Where is the benefit in that if I've already written all / most of my code for your similarity score to trigger a suggestion?