OK I see, for a memory pool it should work. But if you have to deal with a large quantify of small objects, with sizes not being multiple of 16, then you will need some extra space… A kind of 1D Tetris problem 
. This concern differs largely from mine where I want to play on very large chunks of memory and avoid to deal with nonalignment prologues.
Because of the variety of situations, I guess that in the end, a kind of control on the allocator may be interesting to have.