Series pages are easiest to define in comparison to works pages. A works page details a work of fiction or non-fiction, giving a description as to what the work is all about, and a listing of tropes that the work use. A series page, by contrast, broadly deals with every single work of fiction under a specific moniker. So, as an example, the Star Wars page is about all the various Star Wars works of fiction and what those have in common with each other. Someone looking for information on the original Star Wars movie has to go the page A New Hope.
In terms of quality control, series pages became relevant mainly in that, as time went on, it was never entirely clear what was supposed to be a series page and what wasn't. There is no Series namespace- generally speaking the Main namespace is always supposed to be the Series namespace, but this rule is not particularly well-known. This was especially true with pages created before namespaces broadly appeared. Take the Star Wars page, which originally referred to all six of the movies writ-large, which sounds ridiculous today but made a great deal more sense when the wiki was a much smaller place. When this problem was brought to Trope Repair Shop's attention, the issue was acknowledged, even supported- but no one did anything. Eventually one annoyed troper just split the page into pieces personally with less-than-fantastic descriptions, but it was better than doing nothing at all.
This entire issue with series pages is a decidedly non-sexy one. While Trope Repair Shop could get into conniptions over the "true" meaning and popularity of a trope title, series and works page were just statements of facts. There was no meaningful philosophical wrangling over what a person expected when they clicked on the Star Wars Wiki Word, mainly because Star Wars is an actually discrete, definable thing. Subjective opinions, the lifeblood of Trope Repair Shop, simply don't factor into this fact.
Now, while series pages weren't an especially popular subject, longer pages that were not clearly works or series pages still represented a major problem- the descriptions were often confusing, and the example listings excessively long. When I left the forums, they were an obvious problem to fix. One of the first tasks I went about was reorganizing the indexes for Marvel and DC comics to better differentiate between pages referring to a specific superhero versus pages referring to a comic book story that shares its name with a superhero. The Joker, for example, refers to the character, and not the obscure 1970's comic series featuring the character. Technically characters aren't supposed to have their own pages, but as forum discussion over this topic had mainly centered around the unusual nature of story structure in American comics and what this meant in terms of wiki policy, I decided this was a weird enough case that an exception ought to be made or else the specifics would just be rambled over definitely.
More straightforward issues of these clarifications arose in simpler pages. The Pokemon page was the main monstrosity badly needing to be dealt with. The page had grown to be unbearably long and peppered with random plot snippets from four generations of games in the series. When casual tropers expressed concern over what to do about these problems, I suggested expanding the floatbox so that there were pages for individual games in the series as well as the spin-offs. This was agreed to after brief discussion. While this problem had seemed insurmountable in the discussion page, once links to individual game pages were there, Wiki Magic slowly but surely worked to move traffic, and I along with some others managed to move all the individual game examples to their individual games instead of being on the series page.
I'd like to apologize at this point if this explanation is a little tedious and complicated- series pages are a difficult problem to describe abstractly. I often found that trying to explain what I was doing to people was a great deal more difficult than just performing technical page rewrities and splits myself whilst leaving a note stating "here's a page for this specific game in this series that tragically has no useful information on it. If only there was a fan of this game here to help us write it!". The series pages accumulated too much text mainly because there wasn't any other place to put it. In giving fans more pages to write on, I found that they were often more than happy to start branching out their efforts even though they would never get the idea to do this themselves. I once averted a massive crisis with the Starcraft page simply by turning Starcraft II into a stub instead of a redirect. Almost immediately Starcraft fans started started separating their (often spoilery) material into the appropriate page instead of lumping details of both games in the same alphabetical listing.
There was one problem I ran into- by not always explaining what I was doing some individuals started seeing malicious motives in my actions. One user got mad at me for arbitrarily deleting information from the Fallout page when I was actually moving it to the Fallout 3 page (Fallout now being a page for the series in general, not the individual games). Experiences like this taught me to better mind the edit reason box- even if something was difficult to explain, I felt I owed it to people to at least make an effort. If worse came to worse, I could always let the Wiki Magic vindicate me- tropers seldom edit pages that they find to be poorly written.