Redcents are supposed to be provided to the posts that are helpful to you. When you first get to redguides it's likely that a very large amount of posts are helpful to you.
If there were no limits to Redcenting people, then nobody would ever pay for subscription fees through redguides. So it's a way to earn a sub and more based on your amount of contribution to the community, but also limits how appreciative you can be on any given day. Since by giving redcents you earn redcents, if there was no limit someone could just redcent every post until they had enough redcents to pay their sub, or buy krono (when available), get a new coffee mug (which costs to create, and ship), etc.
It's intended to be a system that rewards you for helping, and promotes you giving others redcents who do help. It encourages positive responses to questions instead of flaming and an overall positive experience at redguides. Of course there will always be toxic people, but I like to believe that Redcents plays a big part in keeping some members of the community positive instead of making every answer someone gives RTFM kinda stuff.