Driving a Diesel, i rarely encounter the redline.
Now by how the question i assume you mean hitting the rev limiter?
Im sure that hitting the rev limiter by accident on the odd occasion wont do much hard, thats what its there for, To stop the revs before they start to do damage.
Its more of a pointless thing than a dangerous thing by hitting the rev limiter.
The power will probably drop off quite a noticable amount before the rev limiter, so your gaining nothing in terms of speed by hanging onto the loud pedal.
Now, if you mean red line without hitting the rev limiter, its much of the same thing.
On a mapped car, i would guess that theres still some power left in the redline.
Im sure many of our members get in the redline quite a bit.
Not because they're trying to, just because there is still some peak power to be had from the engine at higher revs