What is the purpose of the ADX token?

The ADX token is used for staking. 

Staking is the process of locking a certain amount of ADX tokens in order to increase the trustworthiness of the validators in the platform by ensuring they have skin in the game.

Validators are appointed for each side of the advertising campaign (i.e. both the advertiser and the publisher nominate an a validator) and they are responsible for processing micropayments per impression on the platform. Appointing validators is a required condition for a campaign on Ambire AdEx to run - they are essential for the operations of our ad network. 

Misbehaving validators are subject to economic penalties (slashing) and thus have incentive to ensure they run uninterruptedly. The more tokens are staked, the stronger the reliability guarantees of the validator network. 

Effectively, staking allows for Ambire AdEx users to have governance over validators and enables better transparency, reliability and decentralization of the entire process.