Though marshal and rogue are both “martial” classes, their areas of focus are almost diametricallyopposed.
The marshal is a class centered around working as part of a group; specifically as its leader, supporting and directing other characters. The rogue is the quintessential solo operator, with features designed to work in a selfsufficient, “lone wolf” manner and its default flavor places it outside the sorts of structures and hierarchies the marshal relies upon. That means that mixing the two essentially means leaning into a leadership role in some kind of shadowy field of work like crime, espionage, covert military operations, or adventuring.
Focusing more on marshal levels makes the character more of a leader, albeit one with some covert skills in their back pocket. Focusing on rogue makes the character more of a solo operator who can lead when the circumstances require it.
[[Synergy Feats for Multiclassers#Marshal w/ Rogue|Marshal - Rogue chains and ideas]]