both EEPROM and ROM (program memory) have limited write capabilities, there is also a definite time delay in writing and reading to these areas, for actual values please refer to the datasheet of the part, the life of these parts will also depend on the temperature.
Writing to RAM is significantly faster and so is suitable for rapidly changing data, EEPROM is best suited for storing data that may be updated occasionally such as calibration data, user configuration data etc.
Whereas program memory is best suited for storing data that will seldom change, such as program code etc.
If you want to expand the RAM of a micro-controller, consider using a FRAM (ferro-electric RAM), these are fast and have almost unlimited read and write capabilities as compared to an EEPROM.