Asks Curved Spaces to synchronize its animation with your monitor’s refresh cycle. The prevents the tearing that would otherwise occur if the program tried updating the screen image midway through a monitor refresh. It also avoids wastefully computing more than 60 frames per second (cf. Frame Rate discussion).
Regardless of what you choose, the Preferences Panel itself synchronizes to the monitor (Mac) or suspends the animation entirely (PC), so you won’t see the effect of disabling Sync to Monitor until you dismiss the Preferences Panel.