Do I have to learn ASP. NET Ajax when learning ASP. NET?

My son has been ill recently and has never been able to learn ASP. NET Ajax. But sometimes I want to learn ASP. NET Ajax?
I personally think: To develop a B/S system, you need to deal with the server in many cases. For example, a page has something, and you only want a small part of it to interact with the server, then use ASP. net Ajax is the best.
ASP. NET Ajax is developed on the application, I think. As if I told my nephew about the crystal head of the network cable, I said there were eight lines in the network cable, and only four of them were used for communication, and it is the position of the crystal head 1, 2, 3, 6, so we need to adjust the line on the 4 and 6 positions, the principle is to reduce interference during communication, my nephew didn't learn the magnetic field in physics, so why do I need to adjust the line? I don't think he can understand it. Similarly, why ASP. NET Ajax is used when B/S systems are developed is because of development needs, which reduces network traffic, saves bandwidth, and improves efficiency. If no B/S tool is developed, how can we talk about ASP. NET Ajax? Therefore, learning ASP. NET Ajax is a deeper stage of development.