At the beginning of time, it was used to help the user decide which 2 products they were contemplating on using, having tested them before, but could not make a final decision. But now I'm not so sure, there's always the same outcome for each case;
- I chose Product A because it's my favourite.
- I chose Product X because it has higher detection rates.
- The OP disappears (not all, but most).
Example from 2011:
http://malwaretips.com/Thread-Emsisoft-Anti-Malware-6-vs-ESET-Smart-Security-5
You could say, you want to buy games console so you compare Xbox One vs PS4, you get the outcome, and then decide you want to compare X1 vs Wii U (or PS4 vs Wii U). There's really no point, am I wrong? If you've picked the 2 common consoles, there's no need to invite another, because they didn't make it in the first round.
It would be really nice to vote for a reason, not just based on our personal preferences. Knowing about the PC user, or system specs, could help make it more interesting, rather than picking what's more popular.
Thanks.