From Synfig Studio :: Documentation
About Stroboscope Layers
The stroboscope layer shows the layers under it at regular intervals and then freezes them for the remainder of the interval duration. It is similar to decreasing the frame rate of an animation while preserving its length. It has a single parameter called "Frequency" (in times per second), which determines how often samples are taken. A frequency of exactly the frames per second of your project will not affect your animation, while smaller frequencies will appear as if you had lowered the frame rate to that amount.
Parameters of Stroboscope Layers
The parameters of the stroboscope layers are: