Many people use RSS feeds as the primary means to access news and information. RSS is anonymous and does not require you to log in.
Though YouTube generates RSS feeds for its channels, it does not display them (to human visitors) or advertise them (to browser software). If you prefer to subscribe to YouTube videos via RSS, then you have to manually construct the the feed URL for each channel.
RSS provides an easier way to check Youtube channels. All that matters to YouTube is that people see their ads. RSS does not block ads and so no problem. Viewers who rely on subscriptions are likely to miss new but not so fresh videos if they don’t log in regularly. (Such videos get folded/wrapped/hidden as newer videos are published.) YouTube RSS feeds can ensure that viewers are more likely to get to know about the existence of a new video.
And, to use this script, you will need the Greasemonkey add-on in the browser. It can be installed from the Firefox/Seamonkey browser add-on search page (Tools – Add-ons from the main menu).