I had mine boil over when I was going very slow (alright, it was the gf who rode it then), but it was at tickover maneuvering balance act so I thought I would fit the fan just to be sure. And the fan kicks in sometimes on hot days when the going gets tough and slow, so it's definately doing something right.
What the fan also does do though, is being in the way when you want to take the tank off, so you have to take the radiator bolts off then undo the top hoseclip and slip the hose off. If done on the sidestand you might get away with not spilling any fluid, but most likely you will have to top up afterwards. Just one of those originalparts Husaberg nuisances you get sometimes. Well, rather have that battle in the garage then the boiling issues when out riding.