Man who was paralysed sues Planet X for £10 million

[Ajax Bay]

I get the idea that it's to do with the compression plug and where the stem clamps on the steerer tube. But is it risky if they overlap so the stem is tightening from outside and the compression plug is expanding from inside at the same time; or is that desirable?
edit: I think I understand now; so the compression plug should be long enough to cover (most of) the length of the stem.

Think this weightweenies forum post is a great resume, with pictures:
"The most common types of damage to the steerer tube come from incorrect torque specs on the stem pinch bolts, [not just too tight]. Suprisingly just as often from being not tight enough. [If the stem is not tight there's movement which cuts into the steerer tube.] The other common type of damage comes from a seized up headset bearing that is not turning with the steerer tube and cuts into it.
"All that being said along with the number of recent posts on steerer tube failures, take the time to check your steerer tube, stem clamps and handlebars and make sure your expander plug is doing its job."

In image above, plug too short for the number (height) of spacers used above so stem clamps on unsupported (but it's not that simple).
There are (3) main purposes for the expander plug (aka compression plug):
1. Installation allows pre-load of the headset before clamping on the stem,
2a. Reinforcing the section of the steerer tube around which the stem clamps,
2b. Reinforcing the 'open' top of the steerer tube around which the stem clamps - where it's structurally weakest and prone to being crushed by the stem clamp (supports argument for a 5mm spacer, as well as having the top bolt bear down on spacer and not (cut) open end of steerer tube).
3. Reinforcing the steerer tube against the force of the rider's weight up and down on the handlebars (and therefore the stem).

 

[Deleted member 121159]

Think this weightweenies forum post is a great resume, with pictures:
"The most common types of damage to the steerer tube come from incorrect torque specs on the stem pinch bolts, [not just too tight]. Suprisingly just as often from being not tight enough. [If the stem is not tight there's movement which cuts into the steerer tube.] The other common type of damage comes from a seized up headset bearing that is not turning with the steerer tube and cuts into it.
"All that being said along with the number of recent posts on steerer tube failures, take the time to check your steerer tube, stem clamps and handlebars and make sure your expander plug is doing its job."

View attachment 715353
In image above, plug too short for the number (height) of spacers used above so stem clamps on unsupported (but it's not that simple).
There are (3) main purposes for the expander plug (aka compression plug):
1. Installation allows pre-load of the headset before clamping on the stem,
2a. Reinforcing the section of the steerer tube around which the stem clamps,
2b. Reinforcing the 'open' top of the steerer tube around which the stem clamps - where it's structurally weakest and prone to being crushed by the stem clamp (supports argument for a 5mm spacer, as well as having the top bolt bear down on spacer and not (cut) open end of steerer tube).
3. Reinforcing the steerer tube against the force of the rider's weight up and down on the handlebars (and therefore the stem).

Great information. Thank you.