Overall,
@Ashrem and others gave very good advice to players in the early to mid chapters. Over scouting becomes less of a problem later in the game, in my opinion, but there are reasons for not completing the scouted provinces. What follows is my experience with playing the game.
Early in the game I would use the target number to enter the next chapter to basically pace me through the chapter and usually do a few more to get another expansion, a plot of land, or maybe two. Another reason for pacing through the chapter was events asking for scouting, relics and encounters.
Once I reached woodelves, I've pretty much kept my scout busy. Coins and hammers were not a problem, but I wanted the land. Scouting time begins to get long (over a day - now it's like 5 days) so continuous scouting helped a lot with keeping ahead of the events and having what was needed to enter the next chapter. In the Halflings chapter, divine seeds become a resource and seed production is directly tied to the number of completed provinces, so having more completed was a good thing. Seed production remains is a struggle for many people even with some building producing them. I'm sure that is a ways off for you and not a concern yet.
With the new tourney method, plots of land placed go into the calculation of your spire and tourney stack size. This is a point of contention with the new method, but my feeling is you need to be in the later chapters before that is much of a problem. Since it's new there is debate as to when and if to place plots of land. I'm just mentioning it here because of the amount of discussion about this and other aspects of the changes which I hope will stay in the Tournament Changes thread and you may want look at that. Be forewarned. Take wading boots. It's a vicious swamp in places.