With a digital communication mode based on a computer sound card, what is the result of feeding excessive audio into the transmitter?

When using a sound card for digital modes, the audio output from the computer drives the transmitter. If the audio level is set too high, it overdrives the transmitter's audio circuits or final amplifier, causing signal distortion known as clipping. This distortion generates unwanted harmonics and intermodulation products, which spread the signal beyond its intended bandwidth. This is commonly referred to as "splatter" or out-of-channel emissions, and it causes severe interference to adjacent frequencies. Excessive audio does not improve the signal-to-noise ratio or lower the error rate; in fact, the distorted signal will likely be harder for the receiving station to decode. While prolonged keying at high power can overheat an amplifier, the direct and immediate consequence of excessive audio overdrive is always splatter.