To explain it simply, the objective of these swap-based ETFs, as with all other ETFs, is to track the performance of a chosen index. These swap-based ETFs will hold a basket of stocks. If these basket of stocks underperforms the chosen index, another party will have to make up the difference in this underperformance to the ETF so as to allow the ETF to fulfil its objective of tracking the index. On the other hand, if this basket of stocks outperforms the chosen index, this difference will be paid to the other party since the ETF is only required to track the index. Nothing more or less.
On the other hand, cash-based ETFs are the traditional type of ETFs. Their model is simpler as compared to swap-based ETFs. Basically, they hold a basket of stocks that replicates a chosen index as closely as possible and this basket of stocks is divided into units where it is traded on the stock exchange.
Why is there a need to understand these two types of ETFs ? This is because there is an additional risk between these two types of ETFs which investors will need to know.
For swap-based ETFs, there is an additional risk which cash-based ETFs does not face and that is counterparty risk. For example, one particular swap-based ETF is tracking an index and for this specified time period, the basket of stocks which this ETF is holding on to, underperforms the index by a significant percentage. As such, the counterparty is required to pay this difference. Now what happens if this counterparty is not able to pay up ? This is one issue which investors of swap-based ETFs may have to consider. However, this counterparty risk is limited to a certain percentage of the value of the fund under regulations so the risk is not that high though it will still be there.
Furtheremore, swap-based ETFs tend to have less transparency. Investors may not know the details behind the swaps such as the value of the swaps and the collateral that are being used for the swaps.
(Taken from Barclays Global Investors)



