Watchdog necessary?

Hi,
i've got one general question.
I have a PIC12F510 doing a temperature control (AD in from an NTC, software-pwm out).
The system has a stable power supply.
All is working fine.

Now my question is, should i add an external watchdog (APX823-44) or not?
I mean, do you think an external watchdog is general necessary/nice to have/unnecessary...or....?

Thanks in advance
Best regards
Norbert