Which holes? The holesin the right dropout are both for looks and 'lightening' the frame (although removing that amount of steel does little to lighten anything)
There are also hole on the little brazon things to run the rear brake cable along the top tube, a cable guide/stop for the rear derailleur cable, a hole in the seatstay bridge for mounting the rear brake, fender eyelets on both the dropouts and fork ends.
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“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
Sugar "Kane" Kowalczyk