Baltic Birch Stability and Strength Relative to MDF Plywood And Use for Jigs

Stability and strength relative to other types of plywood is the short answer. Many cheaper sheets of plywood are constructed with seven or fewer plys; baltic birch typically has 11 plys - sometimes more - which helps create a more stable sheet of plywood. Also, cheaper plies contain voids whereas baltic birch is generally void free. I've seen inexpensive chinese core poplar ply that begins to curl almost as soon as it is cut.

From what I remember, there is a nice article in one of the current woodworking magazines that goes over the various qualities and features of plywood. MDF Plywood is heavier, and it also creates a fine dust that is more dangerous than plywood dust (not that you should spend time breathing fine dust particles of any variety, is not as strong as plywood in certain applications, and doesn't hold screws as well, to name the disadvantages relative to ply that immediately come to my mind.

That said, many woodworkers use MDF Plywood for jigs because it is very stable and easy to machine; I suspect more jigs are made out of MDF Plywood than regular grade plywood but that's just a feeling I get based on nothing more than layman observation.