[mention|faPWDSqCu26g2CHuciEFJw==] CatmullRomDecoder is a class from DOTween as well. If this is troubling to you, I would suggest posting this in the official DOTween thread instead, or contacting its developer directly.
Both CalculatePath() and SetPath() methods in SWS do calculations which are used for initialization and therefore need more resources once in the beginning, but nearly zero afterwards. CalculatePath is a performance heavy operation (this is stated in the scripting reference already) because it allows for recalculating and updating the whole path at runtime. SetPath on the other hand is responsible for initializing the tween you are using for movement on the path, which needs some CPU time for that too.