The benefit of an oval handle is it stops the bat spinning in the hands when you play a shot, eg. maximising your use of the face of the bat.
Handle shape is one the key issues in having the right bat for you in my eyes. Most of the larger brands these days have round handles as most parts on the bat are machined and the handle is often done on a lathe. Whereas the smaller brands will often have an oval handle as they are hand made, and the batmaker would recommend this.
On the subject of bat handles, why is a triple sprung handle the preferred choice for brands these days? I interested in trying a double sprung bat in the future so might enquire about this on my next bat. I know they are different through one allowing more flex etc, but just wondered why its only a majority that do it now...