What is the advantage of using a variable frequency oscillator in a basic CW transmitter?

A Variable Frequency Oscillator (VFO) allows the radio operator to tune continuously across a wide range of frequencies. This provides the flexibility to easily change operating frequencies to find a clear channel or answer specific calls without needing to swap out hardware. In contrast, early or very basic transmitters often used crystal oscillators. While they provided excellent stability, they locked the transmitter to the specific, fixed frequency of the installed quartz crystal. To change frequency on a crystal-controlled rig, you had to physically plug in a different crystal. The other options, such as key click suppression, harmonic suppression, or supporting higher-speed Morse code, are functions of the transmitter's keying filters, amplifiers, and output filters, not the oscillator type.