Andersp - (again my opinion) there is no difference as long as you are not trying to "cheat" the system. There have been people on here who would create multiply accounts (even get them memberships!), play against those "dummy" accounts and purposly lose so their main account can gain more rating points.

(in my opinion) as long as you play a person from the same computer without trying to cheat the system, it won't be a problem.