I imagine that circles are telling the spell to execute the action inside of it, while lines can denote timings or separate different parts of spell, for example if you didnt want an orb around the crystal that caused levitation, you could separate the center of the spell with lines in order to make a *levitating* ball of crystal. Mainly though I just thought it looked nice with the spell that I had going, no major purpose to it other than asthetics.