I do like burning the ships once in a while and wholly agree that it is best done in a fun/practical way rather than a manufactured excercise My example is running/kayaking through the mountains, or running/swimming at the beach when on holiday...I really worked myself in the mountains the other week and close to recovered now.
and to a practical example of "do this but don't ask why": my kungfu school graded us 2or3 times per year. These gradings were typically much tougher than the regular classes and kungfu grading actually took up to a month of classes as we reached the higher levels e.g. beginer grading took 2 lessons (1 for physical, 1 for technical/forms/kata/weapon), my last grading took maybe 6 lessons (each week had a physical and a technical...the technical was always very phsycial as well). this was fun/terrifying/practical burn the ships. Our classes in the weekor 2 after grading were typically a bit easier (recovery) and we easily/quickly stepped up our intensity thereafter. For me, this always demonstrated the link between mind+body. push both and both will improve.