Poor choice of words with regards to the post (anyone is able to buy it but it’s most commonly used in Mythic), but the TL;DR is that at the moment one of the most commonly-used strategies for a very long time involves using a focus macro to set focus to the end of the Demonic Gateway that you’ll plan on using, and then making an “Interact with Mouseover” keybind to mouse over the Gateway focus frame and interact with it instead of having to manually click it when 19 other players are stacked on top of the gateway trying to do the same thing.
With this item you don’t have to use the focus macro/interact with mouseover combo; if you’re in range of an end of a Demonic Gateway you will automatically interact with the Demonic Gateway without having to manually click it as soon as you use the item, which you can also set as a keybind.
The Focus Gateway thing has been used for several bosses. It was mandatory on Mythic Kil’jaeden (the hardest boss ever) and was very very useful for Mythic Carapace of N’zoth. It was helpful on Mythic SLG last tier, too. This tier alone there are three Mythic bosses that borderline mandate the focus macro/interact with mouseover combo: Mythic Soulrender for the chains mechanic, Mythic Painsmith for the last 2 spike walls during each intermission, and, more egregiously Mythic Sylvanas for the P1 and P2 Veils of Darkness (requiring THREE SEPARATE GATEWAYS, so you have to focus the correct end of each of three different Demonic Gateways).
Basically, it consolidates two different and more complex functions into one simple and easy-to-use item, which is only a good thing because now you can use focus macros again and not have to constantly focus new Gateways.