What Are In-App Purchases?
In-app purchases are purchases made from within a mobile application. Users typically make an in-app purchase in order to access special content or features in an app such as power-ups, restricted levels, virtual money, special characters, boosts, etc. The purchasing process is completed directly from within the app and is seamless to the user in most cases, with the mobile platform provider facilitating the purchase and taking a share of the money spent (usually in the range of 30% or so), with the rest going to the app developer.
In the case of BreakingLands, the only available in-app purchases are various quantities of Crowns, the premium currency within the game. BreakingLands is free to download, but has an option for players to purchase Crowns with real-world currency. This type of game is called a 'Freemium' game, as defined by the fact that the game is free to play, but premium items or content are also offered for purchase ('Freemium' being a portmanteau of 'Free' and 'Premium'). As it turns out, lots of people use real money playing BreakingLands, as it is one of the top-grossing games on the Apple App Store.
Is It a Good Idea?
Buying crowns can really speed up your progress in the game by a huge lot! For example, not using the crowns for the sole reason to upgrade your town hall to high level, leaving the defenses at an extremely low level, but use crowns to speed up troop training, allowing rapid attacks and rapid raiding of resources. Another way is to (if you are an impatient person), use it to speed up long building upgrades. Some people buy Crowns for the sole reason of Worker's Houses.