There are a few different ways to play tags. I see the main methods as:
1) Try to exhaust the Runner by having a bunch of tagging ICE
2) Try to surprise the Runner by giving them a tag they're not ready for
3) Try to actively tag them on your turn
I find #2 to be the most effective if you only need 1 tag on the Runner to do what you want to them. (It's not necessarily as good with Psychographics that needs more than 1 tag). Narziss has obviously already discovered one way this tactic works based on his analysis of how Snare! works in his deck. Bernice Mai and the newly spoiled TGTBT agenda serve a similar purpose, and Ghost Branch + Posted Bounty/Breaking News do as well in a different way.
Data Raven's contribution to this strategy can be viewed in a similar fashion to Hollis' work compression concept for Jinteki. The on-encounter tag is the part that's important, not the subroutine. If you put this ICE on R&D in a tag-and-bag deck, that takes away one click they can use on this turn if their plans for the turn include running R&D, unless the Runner already has sufficient protection to ignore Scorched Earth or can bypass Data Raven. If they also need to account for Snare!, that's two clicks they need to remove tags instead of one.
If Data Raven never tags the Runner but forces them to adjust their running strategy to be slower according to this need to clear two potential tags, it did its job. If it forces the Runner to play bypass effects to get around a 4 credit ICE, it did its job. If the Runner simply doesn't run it at all, it did its job. If the Runner doesn't ever keep a tag till your turn with this strategy but has to pay clicks and credits to remove them, it did its job. If the Runner ever fails to account for these tags and dies to Scorched Earth, it did its job.
While I agree on its own it doesn't typically tag the Runner for the Corp's turn, it does definitely tag the Runner unless it's bypassed. That's pretty good taxation on its own excepting the case of tag-me Runners which I did mention already. It's not a good enough reason to spend the influence on it if that's the only benefit you're getting from it though, so it would be bad in a version of this deck that ran the Ghost Branch/Posted Bounty tag strategy, because there's no synergy between those cards and Raven. That said, stacking Data Ravens with the Snare! strategy definitely works, and it's that synergy that makes it worth examining.
Remember that you don't have to win with Scorched Earth - that card is there to punish Runners that fail to abide by the tempo dictation that you're setting for them in the game by using this strategy. If they do slow down to account for the possibility of flatlining, it makes winning via agendas much easier. Narziss himself said he typically wins games via agendas, and the Ravens are a handy tool for that.
Most of the benefit of this comes from having Data Raven on R&D though, because it's an agenda-hemorrhaging murderhole for the Corp. If you don't see R&D as a point of weakness for your deck, then you're probably better off spending the influence on something else. For my part though, it's always seemed like R&D was the biggest point of weakness for any Corp deck during any point of the lifecycle of the game thus far, simply because there are so many Runner cards that destroy you there (Maker's Eye, Indexing, R&D Interface, etc.) and only one Corp counter card (Snare!).