“FPort values 1…223 (0x01…0xDF) are application-specific. FPort values 224…255 (0xE0…0xFF) are reserved for future standardized application extensions.”
In other words, you are free to use values between 1-223 for any purpose you chose, and it is entirely up to you do decide what values your node and infrastructure software sets or looks for and what meaning (if any) it assigns to each value.
Given that airtime is a precious commodity, since you pay for these bits anyway you might as well try to use them to distinguish various types of messages your components send to each other, rather than spending yet more to put that in the payload of your messages. (Granted, given the multi-byte coding, adding an extra byte doesn’t always increase airtime until you bump over the next coding group threshold)