Investing into a faction with your prestige can result in a small boost for the faction/area if enough points are gathered each month. These upgrades can be varied, and their impact depends on how many points have been gathered compared to other factions. This means whilst you may want the beneficial items from a certain prestige store, it will also mean a boost IG for the faction. So choose whom you invest into wisely! Note that prestige investment is not a personal gain, but rather benefits the faction/area the store represents as a whole.
The DM team will aim to implement the prestige boosts within the first two weeks of each new month, can be quicker depending on DM discussions.