Having a real mode operating system (DOS) means that an errant pointer in your program could (and often did) crash the operating system requiring a reboot. Worse, it would scramble your hard disk.

My usual practice was to immediately reboot on a system crash. This, of course, made for slow development.

With the advent of protected mode (DOS extenders, OS/2), this ceased being a problem. It greatly speeded up development, and protected mode found many more bugs more quickly than overt crashes did - and with a protected mode debugger it even told you where the bug was!

I shifted all development to protected mode systems, and only as the last step would port the program to DOS.