I am one of those people who think speed limit changes are an issue. A city or town or highway should have consistent, predictable speed limits, so drivers "know" how fast they should be going, and can intuitively know how fast they are actually driving.
If in a city, I am OK with two non-freeway speeds
Same thing on a urban freeway or rural highway
I am OK with exceptions for obvious safety issues
People will learn how fast they are driving, by looking at the speedo and correlating it with how the vehicle feels. If you speed, well, then you should be consistent when you speed (I'm 5 mph over, usually), so again you know intuitively how fast you are going.
I don't like a huge set of speed limits, where in one town or city you might find 15, 20, 25, 30
It does lead to greater ticket revenue, and never assume that isn't the motive when your local or state/provincial government can't get it together on speed limits. It is far from unheard of for a local administration to set out to deliberately confuse drivers with constant changes in speed limits, but it's wrong and in essence is trading dollars for safety.
Keeping your eyes on the road is way more important, and will lead to much fewer accidents, than trying to fit into some traffic engineer's idea of how fast a given section of pavement is "safe" at.
If you can't build a municipal road that is safe at 25 mph, you (or your civic administration, more precisely) are failing in more ways that matter, and they should be shit-canned at once. They simply don't get it, period.