Disclaimer: This post is mostly about Portuguese roads. Adapt to your own country as needed :)
Some people are retards. Period. No matter what, they will drive on the wrong lane, "forget" to indicate a direction/lane change, or just plainly drive like madmen. Here's a good example:
Others however - as i want to believe - are just misinformed or misled. In the following picture you can see a typical Portuguese highway.
What's wrong with it, you might ask? If it was you driving would you be inclined to drive on the correct (right) lane, or would you naturally assume that the right lane will exit? Why - oh why - would someone create a sign that spans 2 lanes when all 3 will continue normally throughout the highway? Makes little sense to me.
But let's look at another - more critical - example:
These 3 lanes will all continue for the rest of the highway. That being said, why would they put up these signs? Wouldn't it make a lot more sense to have one sign - that spans the 3 lanes - indicating the continuity of the main destination (A5 Lisboa - Linda-a-velha) and then - on top of the right lane - the indication that this lane will let you access "A9 Loures"?
I think with some improvements like this it would be easier to change drivers' mentalities and contribute to safer roads, don't you think?