When the LFO is sync'd to the the clock, it resets with every keypress. While that's OK in some situations, it's mostly annoying.
The LFO is free-running when it is not set to sync to the clock, but then it is not sync'd to the clock.
This is a similar problem as the arpeggiator, which will restart at the exact time of the new keypresses. It be easier for us sloppy players if the arp would start on the first keypress, and then all subsequent keypresses stayed quantized to be in-time with that first keypress.
Same with the LFO...reset on the first keypress but then maintain clock-sync'd phase evolution for the rest of time. Why have a (slow) clock-sync'd LFO that keeps resetting??
Chip