I thought this is a good write up on why air burst rounds are useful.
http://www.navytimes.com/news/2007/06/dn_munitionstest_070615/
Currently, only the 40mm AGLs eg on Bionix 40/50s have air burst capability.
http://www.stengg.com/upload/990Mjmg5MNKCJeWnLRj.pdf
With the new Bionix 2 mounting the 30mm Mk 44 Bushmaster 2 guns, this will provide a significantly improved anti-infantry capability. This will also partly explain why SAF went for the Bionix 2.
Potential enemy - don't bother with foxholes and shellscrapes from now on...