This paper compares the benefits of communication-assisted sensing and sensing-assisted communication in the context of integrated sensing and communication (ISAC). Communication-assisted sensing leverages the extensive cellular infrastructure to create a vast and cooperative sensor network, enhancing environmental perception accuracy and coverage. On the other hand, sensing-assisted communication utilizes advanced sensing technologies to improve predictive beamforming and channel estimation performance in high-frequency and high-mobility scenarios, thereby increasing communication efficiency and reliability. To validate our analysis, we present an example of channel knowledge map (CKM)-assisted beam tracking. This example demonstrates the practical advantages of incorporating CKM in enhancing beam tracking accuracy. Our analysis confirms that communication-assisted sensing may offer greater development potential due to its wide coverage and cost-effectiveness in large-scale applications.