I guess that choosing a decreasingly popular and harder to find calibre like .222 might be a good reason to reload, but as Turnup notes, you'd need to do a lot of shooting before getting any realistic return on your outlay of at least £300 or more, and that's mostly second-hand. Reloading is not a cheap option - it just lets you do more shooting than you would with factory stuff - swings and roundabout kind of thing.

By the time you've bought, say, forty rounds of factory ammunition and shot it to get the cases - what many people do - bought the bullets, and a to-go propellant, plus primers - all of which, apart from the cases, disappears in a bang forever, AND the reloading gear, it will be around £450 or more BEFORE you can begin to reload. That's a lot of factory ammunition... Even the average reloading manual these days costs around £25.