The RS485 CAN HAT will enables your Pi to communicate with other devices stably in long-distance via RS485/CAN functions.
Note:
There are two versions. The only difference betweem these version are the crystal. The old one use 8M and the line added to config.txt file should be:
dtoverlay=mcp2515-can0,oscillator=8000000,interrupt=25,spimaxfrequency=1000000
The new one use 12M crystal and the line should be
dtoverlay=mcp2515-can0,oscillator=12000000,interrupt=25,spimaxfrequency=2000000