The ability to trade synthetic assets is the core value proposition of Synthetix. In contrast to trading "real" assets, trading on Synthetix provides two key differentiating features.
First, synthetic assets don't require a counterparty. Traders are trading against the global debt pool. When a trader exchanges sUSD for sBTC, that sBTC is essentially generated out of thin air. No one sold it.
Second, Synthetix Exchange offers something called
infinite liquidity, which essentially means that higher volume trades won't lead to price slippage, as is common on typical exchanges. However, as Synthetix scales, the "infinite" element is a bit of a misnomer, because trade size is capped by total sUSD in existence which is capped in turn by the market cap of SNX.