Is Radar an absolute necessity?
Like any other tool, radar is a very useful tool but certainly not a necessity in most sailing venues. Radar is helpful in finding markers, avoiding collisions, and tracking small squall cells. In areas where fog is rare, radar is nicety and not a necessity. Offshore, it is helpful to a small crew trying to keep a watch for shipping and other small craft but in clear weather it is a nicety and not a necessity.
On the other hand, If I cruised somewhere like Maine, where there are major hazzards to navigation, strong currents and a grounding can do a lot of damage, I would consider Radar to be a very cheap insurance policy.