A theoretical value is only as good as the volatility fed into it, and that input is the one thing the model cannot tell you. Quoting a contract as 20 cents under theo means nothing until you say whose volatility assumption produced the theo.
The useful application is relative. Price every line on a chain from one consistent surface and the outliers stand out — a strike whose quote implies a volatility inconsistent with its neighbours is either an opportunity or a sign that your surface is stale.
Example: your surface says the XYZ 45-day $55 call is worth $0.78 and the market shows $0.55 bid, $0.85 ask. The quote straddles your theo, so there is no edge — just a wide market. A $0.95 bid would be a different conversation.
Related: black-scholes-model, mid-price, natural-price, option-liquidity