I think terminology has been influenced a bit by the USA ,where A/T has been the norm for years. Many Americans call the handbrake the 'Emergency' brake ( sometimes shortened to 'e-brake' ) and regard it primarily as an emergency way of stopping the car if the foot brakes fail.
Many will routinely park relying just on 'P'. Americans do also sometimes call it a parking brake, so presumably some will also set it when parking, especially if its hilly. But as an exception rather than normal routine.
As sebastiand says with conventional A/T at least ,' P' relies solely on a metal pawl , which put crudely is jammed into the equivilent of the gears . (maybe its a bit more sophisticated than I have described it
) If this pawl breaks or wears , the car would be free to roll downhill.
I usually park a manual car left in gear and also set the handbrake. and with with an automatic I set P and apply the handbrake. Even on a level location. Only exception might be if I intend to leave the car for some time on a secure and level private driveway when I might select P but leave the handbrake off so it doesnt jam due to rust etc.
BTW the electric handbrake switch can still be used as an emergency way of stopping the Mk4. If you flick it up with your finger whilst the car is moving the car will brake. Keep doing so for long enough it will brake to a stop. For a second or so the retardation is quite gradual. So if a curious passenger unexpectedly flicks the switch the driver wont be too disturbed by it. But soon after the rate of braking increases quite sharply to the point the car will stop as rapidly as it would with the footbrake. It stops much better than most cars do in an emergency using just a conventional handbrake lever.
I recommend that Mk4 owners go somewhere quite with no other traffic, and try it out for themselves. Start from a modest speed ,maybe 20 mph/30 kph and just flick the handbrake switch up with your finger. The car will start to slow, but as this increases you may become shocked by just how powerfully the car can brake with just the flick of a finger. . But its easy to just to release the switch and the car resumes as as normal. After trying this a few times I found I control the rate of braking as easily by finger as I could by the foot brake. Obviously this is not the intention, but it did give me confidence that in the unlikely event the foot brakes failed I could still have good control over braking.
It also a good idea to 'initiate' anyone else who might drive the car into this safety feature, and indeed anyone who might regularly travel as the front seat passenger.
I like electric handbrakes. The only thing they cant do is 'handbrake turns' . But few drivers do those anyway.
