You're asking a pretty general question, as there are quite a few variants of cuben and a wide variety of applications. So on one exteme, a backpack using 0.33oz cuben is a failure waiting to happen, while on the other extreme, a tarp made of a 1.5oz is unbelievably durable.
So for a tarp, one might say that:
0.33oz = highly specialized piece of gear, not suitable for typical use
0.51oz = good in reasonable conditions when used by someone with basic skills to use it properly
0.74oz = durable in virtually all conditions
+1.2oz = extremely bomber, difficult to damage even in extreme conditions and with significant user error.
For a backpack, you typically need more abrasion resistance than a tarp, so 1.2oz is about the minimum, 1.5oz is good in reasonable use with reasonable care, and 2.92oz cuben hybrid falls more into the highly durable catagory, while being short of bomber.
Cuben is being used for a huge variety of applications, with varying suitability. Tarps are one of the best applications, as cuben is very strong and not subject to a lot of abrasion (which is its achilles heel) and cuben is a lot lighter than the other options (ie. 1.3oz silnylon). So you can save weight without any major downsides.
With a sleeping bag, you can also use lighter nylon fabrics (as light as about 0.6oz), so you're not really saving significant weight unless you opt for 0.33oz cuben, which is fine for the baffles and okay for the shell, but user care is definately required. The opportunity here isn't nearly as strong as it is with tents/tarps.