Liquidity is extremely important to retail traders because it makes markets fair and efficient. Without liquidity, we would be paying far too much for our trades, making them infeasible.
IVV is a product similar to SPY with the only key difference being that IVV is very illiquid. By trading strangles in IVV, you give up almost 69% of your P/L to liquidity costs, vs less than 5% in SPY.
Liquidity can be the difference between a portfolio that does just ok, versus one that does great.