It used to be that golfers would buy a driver, 3 wood, 5 wood and a set of irons, 3-PW. Even a recent shift to iron sets of 4-GW still leaves the average golfer with two of the irons (#4, #5) with too little loft that many golfers can’t hit well enough to merit carrying them in the bag.
Thus, the common sense goal of set makeup fitting will always be to replace all clubs that the golfer cannot hit consistently well with clubs that hit the ball the same distance, but are easier to hit.
Consistency in hitting the ball well up in the air is key because we can always reduce slice or hook with a length and face angle change (only available in certain club models) in the replacement wood and/or hybrid.
If the golfer cannot hit the 3-wood or 4-wood well up in the air at least 25% of the time, the club SHOULD NOT be in the bag. It is far better to have the first wood after the driver be a 5-wood (preferably 7-wood) that the golfer can hit up in the air more than 90% of the time and give up a little distance, than to keep hoping for the right swing to be able to hit lower-lofted woods. A #9 wood (and #11 wood) should also be considered as both are easy to control and get the ball airborne.
In terms of the irons, we are talking about replacing low-lofted irons (#4, #5 and possibly #6) with hybrids OR high-lofted fairway woods. Within this is also the matter of what lofts and lengths in the higher-lofted woods are going to deliver the same distance the golfer would have gotten on a well hit iron shot.
Length wise, it is just so much wiser to fit hybrids with the same length as the irons being replaced because that leads to a more consistent distance gap between the lowest lofted iron and the hybrid just above it. Loft wise, it depends on the golfer’s clubhead speed. The more the golfer sweeps the ball off the turf (which is 90% of all mid to higher scoring players), the more likely that high-lofted woods will be a golfer’s iron replacements.
Club head speed also plays a role in the set makeup determination. The slower the club head speed, the shorter the distance gap from normal 4° loft increments between clubs. Why saddle a slower speed player with a combination of 13 woods and irons when a 4° loft gap offers only 3 to 4 yards of difference between each club?
Set makeup fitting is really a test of the golfer’s common sense and control over their ego. To play consistently well, golf shall forever be a game of percentages and good misses. Smart set makeup fitting involves using clubs that give the golfer a higher percentage of consistent shots to improve both the percentage of quality shots and good misses.