Sets are always 100% collateralized by its underlying components and redeemable anytime. Most Sets on TokenSets are collateralized by multiple components (e.g. BTC ETH Equal Weight is collateralized by ETH and BTC).
However, Trend Trading Sets are collateralized only by one component at any given time. For example, the ETH 20 Day Moving Average Crossover Set is collateralized by either 100% USDC or 100% ETH at any given point.
Thus, when the ETH20SMACO Set rebalances into ETH, buying using ETH and selling into ETH requires no exchanges of crypto (learn more about how TokenSets uses Kyber liquidity here). Similarly, if ETH20SMACO is in USDC, buying using USDC and selling into USDC do not require exchanges of crypto. This mechanism is similar to wrapping and unwrapping ETH into and out of WETH.
Because there are no external trades:
You are guaranteed to have 0% slippage.
In certain jurisdictions, these deposits and withdrawals may not be taxable events. Make sure to check with your tax advisor.