With DNS-over-HTTPS, your DNS queries are sent to Cloudflare (by default; it is configurable). Without it, your DNS queries are sent to your ISP. The question is which company you trust more with your DNS queries.

Given how often ISPs and/or countries do stupid things with DNS, I think DNS-over-HTTPS is a reasonable default. But some people don't trust Cloudflare with that info, so they use the ISP option instead.

Both are reasonable choices.