1. I use FLASH to store data
2. I know what I am doing, so if I replace a piece of code I know if I can run it immediately or a reset is needed
3. RAM content of '51 is not lost at reset! (see e.g. the Philips' 80C51_FAM_HARDWARE_1.pdf, page 18, right column, just above Table 1).

I have already mentioned the example - the modification of BASIC52 for (A)T89C51RD2 - it "burns" the BASIC program into the FLASH as you type it, then, you can run it, without need to RESET in between.

Jan Waclawek