Since "Signal and System" by Tarun Kumar Rawat is a standard textbook for Electrical and Electronics engineering students, the "useful content" depends heavily on whether you are preparing for university exams, GATE/IES, or just trying to understand the concepts.
Signal and System Author: Tarun Kumar Rawat Focus Area: Continuous-Time (CT) and Discrete-Time (DT) Signals & Systems Target Audience: Undergraduate engineering students (Electronics, Electrical, Communication, Computer Science), GATE/IES aspirants, and self-learners. Signal And System By Tarun Kumar Rawat.pdf