Wondering whether it’s wise to substitute shiplapped rift ash in the back of the cabinet, instead of a frame and panel back.  Here’s the reference:  https://www.finewoodworking.com/membership/pdf/57450/011208048.pdf

F&P back would use rails and stiles 1/2″ thick, with a 9/32″ panel.  I can find 1/8″ baltic birch, or some glorious marine grade 1/8″ ply for $70.  Or I can shiplap nice rift ash into the case’s rabbet.  Each piece 3/8″ thick, 2-3″ wide, about 26″ long.  
Q-1:  If I skip the F&P back and shiplap the back, is it necessary to include a fixed shelf within the case to anchor the shiplapped sticks, or will anchoring top and bottom be sufficient? 
Q-2:  Does it even make sense to embed the shiplapped sticks within the F&P structure?  It certainly can be done, and it might look OK, but it begs the question again about the need, if any, for anchoring the sticks halfway down the case. 
Q-3:  Regardless of the options I’m considering, what is the purpose of two lower rails, with a spline connecting them?

Thanks in advance for sharing gray matter. 
/VR/
-tonto
Hartford, WI