The strakes (or root extensions) only have a secondary purpose aerodynamically. Mainly, they solved a particularly vexing problem on the Rutan canard designs (Vari-eze and its offspring), where the wings were swept and the operating C of G was forward of the wings due to the canard configuration; where to put the consumable load, the fuel, where it can be as close as possible to the C of G.
You couldn't put fuel in the main wings farther aft, because depletion of fuel moved the C of G forward too much, and the Vari-eze already suffered from C of G and main gear placement issues due to the pilot forward, forcing Rutan to use the kneeling camel nose gear arrangement to avoid a tail skid to hold the back end up when empty (a really big problem when there's no tail to speak of, just a propeller).
There was no room in the fuselage for a tank of significant size and still have space for any baggage. That left the sides of the fuselage ahead of the wing leading edge. He could have just put blisters there for fuel tanks, but that makes drag with no other benefit. The root extensions were an obvious and much more elegant solution. Minimal drag increase, and a beneficial aerodynamic effect at high AOA, and plenty of fuel volume that changes the balance very little when depleted.
The presence of the strakes moves the mean area of the wing forward somewhat, but minor adjustments to the configuration take care of that.
"Regular" airplanes can put fuel in the straight wings and don't need strakes of that size and if they are used, there are strictly to improve stall behaviour. Some homebuilt owners, like the Thorp T-18 guys, have experimented with small leading edge strakes to improve high AOA behaviour, but these were only about the size of your hand and are just being used as vortex generators (can't find a pic of one so far).