What are the benefits of the new torment levels?

Even assuming that you want to exclusively run greater rifts, the new torment levels will help you continue to do so. Greater rifts require GR keys that drop from normal Nephalem rift bosses. At higher torment levels, these bosses will drop multiple keys. This table shows how many keys you can get at various difficulty levels, with fractional units being the percentage chance of receiving an additional key.

| Difficulty | T1  |  T6  | T10 | T11 | T13  | T14  | T15 | T16  |
| Keys/rift  | 1.2 | 1.51 | 1.9 |  2  | 2.25 | 2.66 |  3  | 3.25 |

More keys per Nephalem rift means fewer low-experience rifts and more time doing greater rifts. The linked resource also points out the other benefits of the higher difficulty levels including a higher legendary drop rate, more gold, more death's breaths, and more Horadric cache materials.

The new torment levels allow content that does not use the Greater Rift levels to be at a higher level. Think of for example the non existing secret cow level. Or for example the Vault which are created in your current world at the difficulty that the game is in. As each torment level increases gold drop, chance for legendaries, etc these zones gain the benefit of the bonuses these new torment levels bring.

The main benefit that I have noticed from the higher torment levels is the ability to farm faster. Once you are completing greater rift 80 or so, T13 was really a joke. T16 is still easy. However, it is at least more rewarding, given that the magic find and gold find drops were increased.

With this change to the loot dropped from the highest tier torment, at least the loot drop from a single rift is similar to what you would find from a greater rift. In addition to the higher rates of normal loot, the side loot which does not drop from greater rifts is boosted. Death's breath are easy to run out of if you are upgrading rare items trying to get ancient or primals, T16 drops 4 per champion or elite pack now, which helps a lot in farming. The mats which drop from doing each act's bounties are in the same boat.

From my point of view, with players now commonly reaching greater rift 100, it just makes sense that they expanded the torment levels. I certainly think that it improved the game play overall.