I have never purged the activity logs ever since I installed aC and I noticed my DB backups were growing (almost 2 megs), I don't see why it should cause any problem but can I truncate the acx_activity_logs table to reset the logs and lighten the DB's weight ?

Ok thanks for the confirmation :)

In the same spirit, since there is no search index rebuilding would that optimize things to truncate acx_search_index, especially since search works differently with 1.1 ?