No idea about Linux, sorry, but I would guess that scheduled scanning is turned off by default, as not everyone wants to use it, and how would they know when to set a scheduled scan by default, as this would be different for each user?
For what it's worth, in my personal opinion, maybe it's worth running a full scan when the product is first installed, but it's not really necessary to do regular full scans after that, as the product would detect and block any malware or virus if it attempted to execute anyway.
