Hi, like anything else for Li based cells, the diode is just adds a protection layer. If the 3 cells are in fact closely charged, and relatively closely balanced in performance, then the diodes do nothing useful.
If for some reason, any reason, the cells become mismatched, then current can flow from the higher voltage cell to the lower voltage cell. Since these cells are made to recharge, you might normally think that is not a problem, and it might not be if the difference is small.
If the voltage becomes substantially lower in one, then the current into it could be rather high, and of course, that will likely be the one that is mis behaving in the first place.
The IMR cells I think are a bit safer than the nomral LiIons, but I am not experienced with that cell type. What do the r/c guys do? They are the real power users of cells, so that is where I would seek guidance. Perhaps if you ask a mod to move this thread to the battery / electronics section, more responses will come.
