What situation are we talking about? Dungeons? Raids? FATEs/Hunts?
In dungeons nothing will hit hard enough for you to actually want to use DT. FATEs and Hunts are mostly the same, and people really stay far apart there, you may not even be able to hit everyone with a succor.
In raids on the other hand people will stack up for huge raid wide damage that needs to be mitigated (or where it's preferable to be mitigated). To give some examples: Megaflare in T9, Electric Burst in T10, Nerve Cloud in T11, Flames of Rebirth in T12, Giga- and Teraflare in T13, Stomps in Titan HM and EX.
There's not really any content that is hard on healers so far in 3.0, doesn't mean DT will be useless when that content arrives.