I haven't really used always-on studio lights, they're probably easier for metering and focusing because the light source is always there. They're less flexible though as they're usually less portable than speedlights. I gather another disadvantage with always-on lights is the heat generated...if you're working in a studio with a model and they're under the lights for a long time it can get quite uncomfortable. Obviously this would depend on the environment you're shooting in though.
I only recently started using external light sources, and I find speedlight flashes much more portable, so I can use them out and about or in a temporary home studio set up