Modulation is necessary for several reasons:

1. Antenna Size: For efficient radiation, the antenna size should be comparable to the wavelength $\lambda =c/f$. High-frequency signals (low $\lambda$) require practical antenna sizes, whereas baseband signals (low frequency, high $\lambda$) would require антенн kilometers long.
2. Bandwidth Sharing: Allows multiple signals to be transmitted simultaneously using different carrier frequencies (Multiplexing).
3. Power Efficiency: High-frequency signals can be radiated more effectively into space. By shifting the baseband signal to a high-frequency carrier, we achieve efficient long-distance communication.