In "The Time of the Doctor", we see Matt Smith's Doctor go out with a bang as he uses (apparently excess) energy from his regeneration to destroy the Daleks that have besieged him. This appears to be an incredibly powerful piece of destruction, yet seems to have absolutely no effect or consequence on the Doctor (i.e. he still has enough regeneration energy left in order to subsequently complete the regeneration into Peter Capaldi's Doctor, there is no apparent "cost" to this exercise).
This seems counter-intuitive to me, as you would think that a regeneration would have just enough energy for a complete regeneration and no more. Is there a precedent for this in canon that might explain how Matt Smith's Doctor was able to pull such a stunt as it doesn't seem to make much sense?
One thought that occurs to me is that Matt Smith's Doctor may have somehow used up more than one regeneration’s worth of energy in order to achieve all that he did in "the Time of the Doctor", however this is pure speculation on my part. Alternatively, perhaps the first regeneration of a cycle of regenerations (this being a new, 2nd cycle for the Doctor) is more powerful than the others? (Again, speculation.)