Computing them while doing operations is nearly free in hardware, so it makes sense to add them in hardware if you can. It's not nearly free in software, but it's important to do it where not doing it might be obervable in normal flow (tricky things with interrupts are out of luck, even if you always do the software calculation, you could interrupt in the middle of it). In many cases, it's easy to determine the flags aren't observable and you can skip software computation.
Computing them while doing operations is nearly free in hardware, so it makes sense to add them in hardware if you can. It's not nearly free in software, but it's important to do it where not doing it might be obervable in normal flow (tricky things with interrupts are out of luck, even if you always do the software calculation, you could interrupt in the middle of it). In many cases, it's easy to determine the flags aren't observable and you can skip software computation.