Map based campaigns are popular in most gaming systems, and can be useful if not everyone can make every gaming session, or each player has a number of warbands to control. Be careful people dont have to sit around and wait too long before something involving them happens, as that can be a common cause of campaign malaise and player desertion.
I think map campaigns can only improve a game if done well - especially if each retinue plots its own progress on thier copy of the map - which may or may not be subtley different from each other/reality. It can throw up lots of unexpected and interesting twists to a campaign/scenario - as groups are distracted by landmarks hoving into view or decide to follow those mysterious tracks or find thier suspect has already been snatched by someone else - including some possibly abandoning the original plot. Its a great way to move away from linear progression into real sandbox gaming.
Bear in mind it really helps if the GM is on thier toes and has a very firm grasp not only of who is where but on the campaign fluff to allow for the inevitable and frequent improvisiations. It can be a really good change from the usual gaming session, good luck!
Edit: sp