Why you need to "know" your authors
If you know me, you know that I'm all about debating the warrants. So as long as the evidence has good warrants, who cares who the author is? As much as I like warrant debate & despise appeals to authority, there are at least 3 times when knowing who your authors are really does make a difference.
(1) In Cross-Ex.
This is HUGE. Cross-ex can do so much to establish or destroy the affirmative ethos. Being able to answer questions about the qualifications of your authors definitely adds to your credibility and thus the credibility of your case in the judges eyes, while inability to answer those questions can immediately cast doubt on the case. That can directly impact your speaks, since there is a category specifically for cross-examination, and of course speaks can sometimes decide the difference in seeding. Further, as much as we like to pretend they don't exist, there are those judges who vote for whoever persuades them, and I've been surprised by the number of times that cross-ex has appeared on the ballot as a deciding factor in rounds with this kind of judge. Even if it's not an issue in the round, judges like this will often vote for whichever team has the experts on their side, and you want to be that team.
(2) In Evidence Comparisons.
I've already been in multiple debates where the round came down to two directly contradicting studies on the same argument. If you know your authors well, you're in the uniquely advantageous position of being able to explain exactly why your study should be preferred.
(3) In Research.
Having a few really good authors for your aff can be an endless mine for research. For example, for my RPS case, I've consistently been using the same five or so authors for the majority of my evidence. A really good author will oftentimes publish multiple articles and/or studies on the same subject, or even write articles responding to authors on the other side of the argument. Those articles are the ones you want, and you'll miss unless you find some core authors for your aff.
How to "know" your authors
What do I mean by "knowing" affirmative authors? It goes beyond just looking up the credentials of your sources, although that's not necessarily a bad place to start.
First, find out exactly what it is that your authors are advocating, and make sure that it lines up with your aff and that you're not taking them out of context. That may also help you find some extra components of enforcement your plan may have been missing: legal scholars & policy analysts will know a lot more about the necessary components of legislation than the average debater. Second, if you end up quoting an author frequently, find out what qualifies that author to make the argument. I don't mean "oh, he has x degree from y university." You need to know what expertise s/he has in the specific policy field of your aff, whether it's work experience, or academic research. A final thing to consider would be finding out the specific methods your authors used to research the subject, such as computer modeling, surveys, empirical studies, or whatever. It's not essential, but can definitely add weight to your arguments.
In the end, it all comes down to establishing your ethos. Do you want the judge to remember you as the kid who cited that didn't know anything about any of his/her evidence, or the kid who had all the answers and cited qualified sources?