uBOL is entirely declarative, meaning there is no need for a permanent uBOL process for the filtering to occur, and CSS/JS injection-based content filtering is performed reliably by the browser itself rather than by the extension. This means that uBOL itself does not consume CPU/memory resources while content blocking is ongoing – uBOL’s service worker process is required only when you interact with the popup panel or the option pages.

uBOL does not require broad “read/modify data” permission at install time, hence its limited capabilities out of the box compared to uBlock Origin or other content blockers requiring broad “read/modify data” permissions at install time.

Emphasis mine. No background processes, including a website-reading permission does indeed sound more optimized for mobile, where people may have limited resources.