I think, at least for use in insect data collection, it’s the Community ID. One trade-off that all similar platforms have had is the expert-identification vs. ease of uploading records.
For example, BAMONA is an excellent resource for collecting North American moth and butterfly records, but every record must be individually “verified” by a designated reviewer, so there’s a bit of a bottleneck in many geographic regions, as uploads happen faster than the limited reviewers can deal with them. It’s very patchy which areas of the country have fairly complete species lists (my state of PA is in great shape thanks to an awesome reviewer!) vs areas with very spotty lists. But the advantage is that misidentifications (in areas with good reviewers) are kept to a minimum.
By contrast, BugGuide has no real “expert review” process. Anyone can post any photo as any species, and they’re immediately pictured alongside all the other pictures with no “research grade” vs. “needs ID” designation. Misidentifications in some taxa are rampant, and there’s no way to tell if a photo was ID’d by someone with expertise or just posted by someone with no experience as a complete guess.
It’s impossible to have a platform that both allows for easy uploads by all users making educated guesses about IDs and also minimizes misidentifications via expert review, but iNat has gotten the closest to this ideal, IMO. The CID gives a way to distinguish between records that have and haven’t been reviewed and given a “Second Opinion”, while still allowing everyone to easily upload all their records straight to the site with whatever ID they think it should have. It’s not perfect, but it’s the best compromise to date. It’s democratic in the sense that everyone can be a reviewer/identifier, but it still has a way to filter out records whose IDs are based on just one person’s guess. There will of course sometimes be cases where a knowledgeable expert gets incorrectly “outvoted” by less knowledgeable users who fail to change their mistaken IDs, but this seems to be pretty rare, in my experience. In general, crowdsourcing is a good way for IDs to eventually trend toward being correct. (I’ve often wanted to see someone research the percent of correct IDs vs. age of observations for a tough group of organisms on iNat… I suspect that while newly posted records may be misidentified, there is probably an observation age by which someone knowledgeable will have likely corrected mistakes, so older observations may be likelier to be correctly identified. Or do older obs have more misidentifications because the CV was worse back when they were posted? Has anyone tested this?)