Can my files be deleted if I used a beta OS X version? I have downloaded OS X Yosemite beta version and I want to install it but I want to ask if my files - for any reason - can be deleted if I am running a beta version ??

P.S: Please don't advice me to backup my data.
YES

With beta software there is always the risk of bugs which may be more severe than those in a version available to the general public. So the advice to "always make backups" is valid even stronger if you use beta software (may this be an OS, may this be just any application).