Reference clock in FM receiver chips (si4735)
For an ultra-low-power design, only low-frequency crystals are usable, because with the frequency increase the current consumption increases significantly. The article The Strengths of 32.768 kHz Oscillators is undoubtedly a commercial, but I venture to mention it because the article excels, first of all, the technological advantages of generic tuning fork crystals.
Their chief application being RTC circuitry, the tuning fork crystals operating at 32.768kHz, due to their excellent short-term, long-term and temperature stability and low power consumption, govern also the other time-critical functions of many common devices, among those are frequency synthesizers. The frequency synthesizer is an essential component of modern radio transceiver chips.