Yeah, you can't always do it smoothly via ssqc.
Note that a few engines will automatically smooth out angles if you fixangles them in each PlayerPreThink (including both FTE and DP). Also note that such angles are often limited to 256 graduations, even if interpolated.
CSQC gives a way to avoid the graduations. It also means your angles will be correct despite prediction. If you're not using prediction, using an engine with setangles interpolation, and are using an engine with extended WriteAngles protocols (player-angles-only like QW will be just as corse), then csqc for this is overkill.