There are 2 types of voting. First one is done by commiting XPD tokens and is used to make faster decisions for managing the system(reward boosts, fees, bonuses,...). The second option is voting through miners(locked) XPD tokens. It is effectively the consensus mechanism of the protocol that allows upgrades of the entire system in a decentralized manner. The long term miners in the protocol get to decide on the future of the protocol as well as manage the treasury wallet. The longer the time-Miner, the greater weight(power) is assigned per each token minerd.