The problem is it can be inherently wrong as it is after all just a script and confuses drivers because they follow it literally and it does make mistakes because in a lot of cases in will follow the first exit of a junction which isn't always correct.
Using the example from above junction 27 on the M25 takes you onto the M11 northbound.
The Nav can get in a pickle as there is two ways you can do it.
You can stay in the 1st lane which puts you on the exit to the M11 southbound as this is the first exit in front of you but it will then tell you to go into the right lane to take the exit to M11 northbound as there is a little straight where it forks into two for M11 southbound and northbound. This is logical for the Nav as you are taking the first exit of the junction. The problem is traffic is rubbish on the 25 at the best of the times and people nearly crashing into each other because they are switching at the last minute.
Yet if you just used your eyes and looked at the sign a mile before the junction you would see to stay in the second lane and take the "2nd" exit of junction 27 and follow that around to M11 northbound in a smooth single swoop.
You get junctions like this all over like where the A46 joins the A50 or the A500 onto the M6. I could go on for hours really. People just blindly following the Nav where it is clear as pie on the signs a mile back on the road.
A feature on my Garmin has the roads in list format and the miles before I come across them. I haven't really played much with Google maps to see if they have something similar as in default they only show your next turning but this is the best feature for me as I know my route 100's of miles Infront.
Motorways and a-roads are probably where it's least needed because they're generally well signposted. All other roads however can be an absolute gamble, especially if driving around city centers where road markings can be useless because there's always cars either stationary or driving over them, and by the time you do see the road marking you could very well be in the wrong lane.