It discourages strategic bidding and encourages people to bid what they actually think the gold is worth. Of course, you can't force people to bid that way, just create the incentives.

An example of the difference would be that lets say I think the gold is worth 1 XMR. So I bid 1 XMR for all 10k. No one else thinks it is worth more than 0.5 so that is the highest losing bid. Under the old rules I pay 1 XMR, which penalizes me for bidding my actual belief (I could have bid 0.5 or 0.51 and still won). Under the new rules I pay 0.5, which does not penalize me.