I haven't used uMatrix, since I use Firefox, but I can speak for RequestPolicy, which is kind of the same thing basically AFAICS. It's very very very rare that I end up whitelisting everything that's requested on a site. The more you use the extension, the more you learn to recognize what domains you need to allow in order to have the site working as intended, and this way you end up building your own whitelist: allowing requests from a domain is a one-time only thing most of the times (additionally, there's an extension you can install that syncs your whitelist to your Firefox Sync account).