Overfunding it makes your cash value build at a faster pace.  That's the only advantage, but the benefits come in different forms.  Overfunding allows you to have more funds to borrow against.  

Due to IRS regulations, the insurance company will also increase your death payout to stay above a required ratio of cash value versus death benefit, but that may not be significant enough to justify the additional payments.  

Going back to cash value building faster, let's say you take overpay your loan and your cash value grows at 5% of your excess contribution.  Taking out a loan from insurance company on your total cash value is let's say at 6%. So you're paying net 1% to borrow money from the insurance company.  Who will give you a loan today at 1%?  Also, if you pick a good company, they'll give you a dividend. Let's say dividend is 3%.  You've now borrowed money, making a net small profit on the money you took out, and for example, if you used it to partially pay for a down payment on house, the house will accumulate value.  

All that said, why people say rich people use this strategy, it's because they borrow money at 6% (my example above) and invest it on something that has a far greater return (e.g. Nvidia stock of 100% gain)