Previews concentrate on who starts. The substitutes are the more revealing selection, because a bench is assembled to solve problems the coach expects to face.
A bench is a set of prepared answers
Competitions permit a limited number of substitutes from a named group, and every place on that list costs the coach a different option.
Naming two center-backs among the substitutes signals an expectation of defending a lead or of coping with an aerial threat late in the match.
Naming several attacking players instead signals a coach who expects to chase the game or to face a defense that will tire and open up.
Backup goalkeepers consume a place regardless
Almost every bench includes a reserve goalkeeper, which is a place that will very likely never be used but cannot safely be omitted.
That reduces the effective bench by one, and in competitions with smaller squads it forces genuine choices between covering a position and adding an option.
Where a third goalkeeper must be registered, the constraint is tighter still, and it shapes the composition of the entire matchday squad.
Substitution rules changed the calculation
Allowing five changes rather than three transformed the bench from an emergency provision into a planned second phase of the match.
Coaches now select substitutes expecting to use most of them, which favors players who can enter and change tempo rather than direct positional replacements.
Clubs with deep squads benefit disproportionately, since the rule rewards having several players of similar quality rather than one strong eleven.
Absences from the bench are information too
A senior player who is fit and not named is being rested, disciplined, or protected ahead of another fixture, and the reason is usually inferable from the schedule.
A young player named for the first time indicates either a shortage in that position or a coach signaling a promotion within the squad.
Both are visible about an hour before kickoff, which is early enough to change what a preview should say about how the match is likely to unfold.
How to read it quickly
Count the defenders, midfielders and forwards on the bench and compare the balance to the opponent's likely approach, since the coach has already done that comparison.
A bench weighted heavily toward one phase of play tells you which half of the match the coach considers decisive, which is a sharper claim than most previews make.
It is also a claim that can be checked afterward, since the substitutions actually made either follow the pattern the bench implied or reveal that the match went somewhere the coach had not planned for.