The EFM32LG/WG has three sets of clock input pins. Uses are as follows.

• XIN, XOUT: Clock for wireless IC
• HFXTAL_P, HFXTAL_N: High-speed clock for MCU
• LFXTAL_P, LFXTAL_N: Low-speed clock for MCU (32kHz)

A wireless IC clock is absolutely necessary.
As for the clocks for the MCU, a high-speed clock of 28MHz and a low-speed clock of 32kHz are built in, so if there are no problems with the frequency and accuracy, there is no need to supply clocks externally.