Despegue
What you are advocating is fine in most places, however in places where there are obstacles further down track, the analysis may well have selected an acceleration altitude that is below the height of the obstacle/s.
In some cases the analysis program calculates a weight that is predicated upon accelerating at a set height, cleaning up and climbing clean over the obstacle. Extending the second segment may lead you into the situation where you extend the 2nd segment distance to the point where you don't have the required obstacle clearance because you had to reduce thrust to MCT before getting the flap all the way up.
This problem is exasperated by 5 minute engines vs 10 minute engines, however the principle remains the same.
Obviously where there are no distant obstacles these issues are not so important, but you end up with a set of rules that apply in some cases, with another rule for other situations - to my way of thinking you would be better having one set of procedures (ie relating to acc alts) so that you didn't have the potential for confusion at a critical moment.