This issue has come up a lot in #wowuidev over the last several months. There is a WoW UI dev in there who kindly answers most of our questions and takes note of issues.
A lot of different people have argued this point with him, and I think I can quickly summarize his two main arguments for those curious:
- They've greatly improved garbage collection performance recently, and have monitored the performance involved in using tons of small, disposable tables under the new GC implementation. It is an incredibly small performance hit.
- Tables help normalize UI implementation and are especially useful in cases where the number of returns is variable. The other thing seems to be preference. It seems like the UI devs prefer the syntax where you pull down a table of results and use the individual parts you need rather than doing 'local _, _, thingA, _, _, _, _, thingB = SomeRandomApi()'.
I'm just paraphrasing here, but this is what I recall. In any case, it seemed like an issue they were -not- willing to budge on. One person was very adamant that they should introduce a function to return this one argument he was interested in because he polled it very frequently and was now required to pull down a table (Spell name, maybe? I forget), and the UI dev was not willing to entertain the possibility of introducing specialized functions to bypass the table returns. He was fairly adamant that there would be a near zero performance impact due to the speed of simple table disposal.
The only annoying part here is that it is basically impossible for us to independently verify their claims because as noted in previous posts, you can't really perform a partial GC on demand and record cycles spent or reliably compare the results. The only ones who can really know the exact impact of these changes are Blizzard themselves.