Compared with drifting through a stop sign at 0.3 mph, filtering is legal.
Filtering sometimes infuriates drivers.
Sometimes, in only some situations, filtering is safer than not filtering- for example, it can get you through a dangerous section near an intersection while no traffic is moving, but not filtering will put you in in free-for-all with maniacs with paramilitary vehicles.
On the other hand, sometimes it looks totally cool to filter, but it is not.
You might want to avoid filtering in the door zone at a speed where a passenger jumping out would mean a serious incident.
As far as I can see, if you filter past cars at a light, those cars are still not legally allowed to pass you without giving you 4 feet of clearance - even if you take the lane after filtering. In reality, you cannot expect to be given that clearance.
If you filter and then take a lane, you can expect < understatement> some hostility from drivers and society at large.