So far I haven't run into any limitations per-say, but just depending on how complex the motion is it may take some time to get them all in , meaning how many individual animation commands will be needed for each section ( or degree or angle ) of motion.
I modeled a crank and rod assembly pretty easily, just took time since I had to think and calculate what the path of the crank end of the rod would take. (big end making a circle while rotating and moving linear...etc.)
Now I am modeling the path for a rotary engine... thats entirely different!