If Cloud information on files helps Avast make for better protection, then i'm all for it, as All Av's are doing this type of thing nowadays. As No personal identifiable information states is sent, then that has no problem with myself, and For the top notch protection from internet based threats, then that is great...
When using an Antivirus you have to have some trust when using the programs...I'm sure Microsoft MSE/Windows Defender do same thing or something similar with there Malware Active Protection Service built into there antivirus. Though personally I tend to trust Avast more myself, as they've been in business in the security field numerous years...