Some think emerging markets is more risky but will have a higher growth rate (= higher rate of return) in the future. That would suggest overweighting emerging markets to increase your overall international rate of return.
One advantage of owning the three international "regional" funds instead of total int'l index is to get the rebalancing alpha. Assuming the returns of the three regional funds are sufficiently uncorrelated, there's a good chance you can increase your overall international return by rebalancing to a target allocation of the three components (ie - Europe - 55%, Pac - 30%, EM - 15%). Rebalancing will force you to sell the outperforming (overvalued) asset(s) and buy the underperforming (undervalued) asset(s).
A third reason would be to get the foreign tax credit. If you own the 3 regional funds in a taxable account, you can take as a credit on your US tax return any foreign tax paid by your fund on your behalf. My understanding is the consolidated total international fund at Vanguard does not allow you to take this tax credit. If memory serves, this amounts to approximately 0.25-0.5% of the amount invested per year.
Then there's the issue of portfolio size. You'll be paying $10 per fund with less than $10,000 in it. If you have 15% allocated to emerging mkts, you'd have to have a total of $66,667 in the three regional international funds to completely avoid the $10 fees. In contrast, the total international only requires $10,000 to avoid the $10 fee. Each fund has a $3000 minimum purchase as well. That may make your Em. mkts part of your portfolio overweight at first.
A benefit to owning the total international is you don't have to pay the 0.5% purchase and sales charge for the Emerging markets fund. However, if you are a long term investor, I think the tax savings for holding the 3 regional funds separately will offset this initial purchase fee, assuming you are in a taxable account.
Personally, I've opted to own the three regional funds separately in taxable accounts and intend to rebalance to my target allocations.
Overall, it may be splitting hairs a little to favor one approach over the other. The more complex approach has more benefits in my opinion, but it sure is easy to buy a single fund and let the market do it's job.