It has its value both ways. For the users it is not only a way to keep track of the hacks you've installed but if there are any updates to the mods those who've clicked the "Install" link will get an e-mail. For the authors, it gives their work a bit of validation. Knowing roughly how many users have installed their hacks the authors get a sense of what is wanted and/or demand. With that information the authors can keep up with the trends of the community.
There are more reasons but I must attend to the other hot topics...