[TrudyM]

I asked my husband the engineer about this one. He said
If you use Ikea cabs they mount on a metal rail. (attached to the wall with the afore-mentioned correct screws) The load is then spread across the width of the span instead of a point load at the screw location. If you will load the cabs with really heavy stuff and boxes on the top etc. the placing of a support below as mentioned is a great idea.

Hope this helps