For starters, it prevents some censorship and filtering, because it is usually done on DNS level, like in UK.

ISP can to see, to what domains you have connected, but most webpages use CDN servers like cloudflare, so while he could presume that you have connected to piratebay, there is no guarantee. It could be just an AD on some webpage or a linked picture, because each time you connect to any webpage, your browser makes connection to 30-50 other webpages, so it is not as straightforward as DNS, so an encrypted helps.