The mid is not a price anyone is offering — it is an average of two prices that are. On liquid series it is close to fair value and often fills. On wide markets it is a fiction that hides how much you will actually pay.
Good practice is to work orders from mid and walk toward the natural-price in small steps, rather than paying the natural immediately. On multi-leg orders the mid is computed on the package, which is usually far more achievable than the sum of individual mids.
Example: an XYZ call quotes 1.20 / 1.40. Mid is 1.30. A buy at 1.30 that fills saves $10 per contract versus paying 1.40. On a ten-lot that is $100 for thirty seconds of patience — and if it does not fill, you can still pay up.
Related: natural-price, nbbo, spread-width, price-improvement