It’s like Reddit, as an link aggregator (Wikipedia said “social news aggregation […] website”), but federated (in the Fediverse), as in it is not centralized and built upon many instances of Lemmy, not just one centralized website like Reddit.

IDM only does direct downloads, or taking over downloads after waiting the timers or clicking the download button.

You can just give the download URL to JDownloader2, either direct or on a file host, and it will do the job. It supports many file hosts, which may be dealt differently from one to the other, such as needing timeouts, donwloading from folders, handling passwords (it would ask you for it), solving CAPTCHAs (it would also ask you for it), and so much more. Everything would be dealt and you get the file just from the URL you gave it. It’s a versatile tool.

Yes, because it can be an indicator of reputation of someone.

No, because of the ease of getting it, as well as it can be a basis of someone’s ego.

Actually, any number that is attached to person has the same set of pros and cons, except of the ease, persumably. This includes SO’s rep system, Reddit’s karma system, YouTube subscriber/view/video count, Twitter followers/post count, etc. Adding karma system to Lemmy may have its side effects, but even there isn’t one, it may not matter since Lemmy has post and comments counts.

EDIT: In the end, when I’m reading Reddit or Lemmy, I gave no attention to the karma, and instead the vote count of the post/comment itself. Call me ignorant, but whatevs.