Main idea is to use `ternary logic` in these hint flags: `ON` / `OFF` / `DEFAULT`. This is done to make these flags **optional**.
Optional flags means that there are no `DENY CPU WRITE` decision will be made if you specify other flags without `CPU_WRITE` flag. Ternary logic allow to bypass this decision from the user. Binary logic doesn't work here, because it **requires** to specify **all** flags and don't allow to "skip" some of them (because "missed" flag is a "false" flag in binary logic).
So if you don't specify some flag, then some default value should be used. Default value in these usage flags is not a constant by design (for example, like default NON_ISOLATED in image filters), it depends on many other factors (current HW/SW configurations, configuration options).

PS: There are missed `USAGE_CPU_READ_ONLY = CPU_READ | CPU_NO_WRITE` and `WRITE_ONLY` flags.