The basic thing to think about, is how you want to use tagging on your site.
Gaming intends to tag any game's title. Yes, it will eventually result in odd tags like [atom-zombie-smasher] or [fish-squid-time-machine] or [the-great-gatsby], but for us, the game's title is the core thing that people sift through information on. It does cause problems if a game doesn't get enough questions (it needs 2 within 6 months), or if the title is long (let's not get into the 26 letter titles), but we work to handle those issues.
SciFi and Fantasy, on the other hand, does a variety of things. As appropriate, the tags go for author, series, universe, or work, resulting in the individual names only for isolated cases. This allows them to focus on more prominent elements than being narrow, as the narrowness isn't as necessary.
As such, it is viable to tag every title if that is decided on, but it is by no means necessary. The site may be able to operate with a less granular tagging system.