Fitters use lie-angle tape to see if the sole is contacting the ground at the centre. A practice-range mat can reveal the same thing with the green marks on the sole.
Generally, if the marks are towards the heel, your shots will start left of the target (for a right-hander), and your irons might be too upright. If the marks are towards the toe, the lie angle is too flat, and misses will start to the right.
According to Titleist research, a lie angle on a 7-iron that’s 2 degrees off will produce a miss that’s seven metres wide of the target.
The misses for short irons aren’t any better.