Theoryhammering is the act of theorizing what may or may not be good in games of Warhammer 40,000. It should never be given or taken as advice, it is a starting out point for testing through math and playtesting whether an idea can be used effectively in games.
Timmy: "If I take the Landstrider Warlord Trait for my Knight Gallant it will have an easier time getting into close combat because it can add 2" to its Charge distance."
Spike: "If you take Ion Bulwark as its Warlord Trait instead your Knight Gallant will be more likely to survive shooting and then getting into combat because its invulnerable save will be better against Shooting."
Timmy: "But then I can no longer add 2" to the Advance and Charge distance of my Knights within 6" of the Knight Gallant."