If you know the authors of your specific area of research, arXiv is a nice way to read their new papers when they are (mostly) done but the submission to a journal is not finished yet.
Despite the imperfections, I found arXiv indispensable for my research. In particular, mathematics has a slow peer review cycle (it's hard to read and understand, and many referees require that they fully understand a paper to accept it, which imo is a little flawed, but that's the culture). I had several papers that were under review for more than a year (single journal, only one round of revisions), and arXiv was my only showcase. Both works ended up very highly cited, but publication delays would have been an even bigger problem if arXiv wasn't there.