Can someone please tell me why bitcoin mixers seem typically seem to have both a darknet and clearnet address? Maybe I'm missing something obvious, but just now I can't imagine what the point is.
Those addresses are only reachable via TOR. Some users who want to stay as anonymous as possible may prefer to use them (and TOR) instead of the regular .com domain.
".onion names are used to provide access to end to end encrypted, secure, anonymized services; that is, the identity and location of the server is obscured from the client. The location of the client is obscured from the server."
Source:
https://www.quora.com/What-is-an-onion-site-and-why-are-they-used
And clearnet addresses for those who don't want to bother downloading TOR and setting it up.