Global statistics don't matter. What matters is current & potential visitors to your site. And how badly you want them served.

A professional B2B car parts dealer has a very different user profile than say, a local news site in rural Africa.

A site selling concert tickets (for popular artist) probably won't care if site doesn't work for 5% of visitors, the tickets will just take a bit longer to sell out.

But otoh I'm sure there's many businesses out there who wouldn't mind a 2..5% bump in conversion ratio for very little effort.

Personally I don't care. If I'm out to buy something online & webshop doesn't work or takes too long to load, my purchase goes elsewhere.

And ofc government services should be very conservative in this respect.

Edit: and yes, graceful degradation. It's ok if site doesn't look as intended but is still useable for that 2%. And eg. I love that some news site have a text-only lite version.

With images specifically it’s a tradeoff. For image heavy sites like mine, the performance gains provided by webp for the 96% outweigh the potential degradation for the 4%. We get a fair amount of support tickets but not a single ticket has said “I can’t see your images on my X device” since switching to webp (~6months ago)