Just a guess here, as I'm not a programmer of any type, it likely has to do with all actions that either/ both require computation and/or take up space in blocks, which requires resources from the servers running the Steem blockchain (witnesses), both in terms of space and computation.  Because the number of actions that the blockchain can handle all at once are limited and some actions require more resources than others, such as posting comments compared to sending Steem from account to account, they are allotted proportional Resource Credit (RC) values.

One thing this will help with is spammy comments and posts, since most accounts that do these types of actions are low in SP and tend to use the strategy of making many posts per day to create a type of "net" to hopefully get lucky on a few votes.  Now that the blockchain better accounts for how many resources are being used up by these types of actions, those low SP accounts won't find it as easy to pull off that type of strategy, and that translates into less "trash" (spam) on Steemit and other Steem DApps.  At least, in theory.

As we all move ahead in 'oneness..."Reversing Forward. Future Is History"