1. persistence, which obviously is hurt by them running out of money. Dropbox links apparently die eventually, static websites bitrot, etc. Things put on arxiv can be trusted enough to put links to them in papers, if needed.
2. Discoverability. Pre-print archives send out digests (usually people subscribe to particular areas). It's a low-effort way to distribute them. Related, by having things semi-centralized, it's easier to discover papers (they get indexed by google scholar, for example...).
1. persistence, which obviously is hurt by them running out of money. Dropbox links apparently die eventually, static websites bitrot, etc. Things put on arxiv can be trusted enough to put links to them in papers, if needed.
2. Discoverability. Pre-print archives send out digests (usually people subscribe to particular areas). It's a low-effort way to distribute them. Related, by having things semi-centralized, it's easier to discover papers (they get indexed by google scholar, for example...).
Maybe other benefits? Not sure.