Half a megabyte is a lot of image
Under 500 KB you can keep a photo at 2000+ pixels wide at quality 80–88 — genuinely difficult to distinguish from the multi-megabyte original. This is the right target when quality matters but the raw file is impractical: photography portfolios, client deliveries, email attachments, marketplace listings with zoom.
The main event here is what you're saving: a typical 6 MB phone photo becomes ~400 KB — 15× smaller — with no change most people can detect. Ten attachments stop being a 60 MB email that bounces.