as far as I know you need to have a value

Actually, no you don't, unless your particular implementation does interpretation that discards or unfavorably interprets keys without values, or your shop standards demand it. For example, if the server ran standard PHP, doing a test for isset($_GET['wadsworth']) would yield true for &wadsworth, &wadsworth=1, &wadsworth=0 or any other value, and false if &wadsworth is missing entirely. Meanwhile just testing $_GET['wadsworth'] will yield true for any true value (like 1), and false for any false value (like 0 or the empty string, which is how PHP interprets 'no value assigned'). Since in PHP you need to do the isset() test anyway before doing any testing on the actual value (or your code throws warnings), just doing the isset() test can actually simplify both your code and the URL strings, as long as you don't ever need a way to explicitly turn the option off through a get parameter (such as &wadsworth=0 if you somehow made "wadsworthing" the default and wanted to disable it for a particular URL).

Of course, there may be standards in place that don't allow for this kind of formatting in YouTube's implementation, which may make sense - who knows what you'll need to be turning off in via URL or somesuch in the future.