When to use MCLR, WDT, PWRT, BODEN, CP, CPD, etc

Okay, These functions (fuses) must have certain times when one wants them enabled nor not enabled. How do I know when being just new at this whole thing?

For example, when do I need WDT enabled and when does it not matter at all?

Three things that have me puzzled more than usual right now are the CP and CPD fuses. When do I want them enabled and when do I want them disabled? I don't want to lock myself out of the chip or make data in the eeprom impossible to read or write to.

Also, I find this particular phrase in the data sheet for a PIC12F629 particularily troubling:

<b>the bandgap calibration bits are factory programmed and must be read and saved prior to erasing the device</b>

So what the heck is going to happen when I make my first attempted at programming the chip then need to erase it and try again when it doesn't work? I don't see any function to save this information. Am I going to be tossing chips in the garbage when I try to erase or re-program?

Thanks.

Bart