There are those that do and those that don't; keys that is. Personally I do. If you get the cutting parameters right you're not likely to jam the cutter. And that means feeding at a decent rate, at least 2 thou per tooth and preferably 4 thou per tooth. When I started horizontal milling I used a very slow feedrate. The whole mill shock, which is good going for a machine that weighs 3500lbs. Upping the feedrate to a proper value cured the problem. For reference my horizontal mill is gear driven, and has a 5hp motor, so you're not going to stall it, or at least I haven't managed it.
As an aside there are two types of slitting saw, fine and coarse tooth. In this picture the saw bottom right is fine tooth, the rest are coarse tooth:

Fine pitch slitting saws are only suitable for shallow cuts, like screw slots, otherwise the swarf jams in the gullets. Coarse tooth slitting saws are happy taking deeper cuts, ½" is not unreasonable.
Andrew
Edited By JasonB on 21/08/2017 09:10:57