regulatory.bin is read by crda upon the Linux kernel's request for regulatory information for a specific ISO / IEC 3166 alpha2 country code.
regulatory.db is a newer, extensible database format which (since Linux 4.15) is read by the kernel directly as a firmware file.
The regulatory database is kept in a small binary format for size and code efficiency. The regulatory.bin file can be parsed and read in human format by using the regdbdump command. The regulatory database files should be updated upon regulatory changes or corrections.
http://wireless.kernel.org/en/developers/Regulatory/