Resistive on-die termination
Suppose 50% of energy is reflected. Do you care? That is a 3dB impairment to Noise Figure and to SNR. Its a big deal. Yet many ESD diodes/structures will suck up this much of the incoming energy.

Suppose 10% of energy is reflected (~ 0.5dB). You see wiggles in the VSWR plots but who cares? The dataeye may care. And thus you care. Depends on the narrowness of the notches and peaks.

Suppose 1% of energy is reflected. In a 256-QAM system, with jitter and random noise as impairments, that 1% can be a big deal.