It's so much fun to know your limits, and really useful when you're prototyping parts.
I like modeling things like little tool holders to fit inside the railings on my printer, so sometimes need to print a couple of them to get the size just right. When doing these tests usually I print 0.6 nozzle, 0.3 layer height at 300m/s and 3000m/s^2 accel. Parts usually don't come out super pretty, but more often than not I end up using the final "test print" rather than reprinting it at more reasonable speeds because I just need it to work, not look nice.