Some sites are prone to drop connections when the transfer slows down (and dialup is prone to slow down for things you don’t see, such as your package manager fetching in listings from the repos). Browsers like Firefox will stop trying when that happens; wget will retry the fetch, picking up where it left off until the file is completely in or the retry count is exhausted. You can even halt the fetch with ^C to free up the connection, then redo the command later, putting a ‘-c’ between ‘wget’ and the file’s URL, and wget will pick up where it left off, fetching in only the part which it hasn’t got yet.

Also, browsers are prone to stumble and freeze when there’s a file fetch going on as well as a new page to browse. With wget doing the fetching, the browser is a lot quicker in moving from page to page because it isn’t timeslicing between the two tasks.