I've seen a few photos recently of escapements with traditional, "screwed" or weighted balance wheels, but also a regulating device, swan-neck or otherwise (e.g. Rolex, JLC, Patek, even an old Benrus from the '50s)). Why both? If the purpose of the weights is to regulate the rate, as is the regulating lever, isn't one or the other redundant?
Are the weights (either traditional or adjustable-mass) to adjust for isochronism and the lever for rate? Or does it just look cool?