One more idea to add: %att tends to show a huge "jump" in %increase in damage at the initial stages when you have little to none to begin with. This phenomenon is rather prevalent due to the fact that everyone is naturally deficient in %att; it's more difficult to obtain, and it's not innate for most classes. Nevertheless, you should not be misled that two lines of %att will always trump every other combination of potential, as it also has a capacity (where it begins to yield a diminishing increase).
It is therefore completely plausible for two lines of %boss to be superior to two lines of %att, for example, even if you have a large amount of innate %damage to begin with. It is also important to note that %boss and %att come in different "bulks" (30/35/40 versus 9/12 at legendary), which allows for a certain degree of flexibility in different scenarios (such as tolerating a loss in %damage when you cubed with Hero's Gloves in mind, but ended up with Mu Gong's Gloves for the week).
This idea can be extended to a comparison of %stat and flat +stat boosts, and bonus cubes are a great way to provide these immediate and/or long term "fixes". In the end, if you want to optimize your character, you need to take a holistic approach; see what you have, recognize what you're lacking, and make a conscientious decision.
The relative values of potential lines are constantly changing (so long as you keep upgrading). Black cubes provide you the luxury of keeping existing potential, so you can always aim for an instantaneous %increase, no matter how small, without risk.
Whether the cost is worth it, however, is a different topic of discussion.
It is therefore completely plausible for two lines of %boss to be superior to two lines of %att, for example, even if you have a large amount of innate %damage to begin with. It is also important to note that %boss and %att come in different "bulks" (30/35/40 versus 9/12 at legendary), which allows for a certain degree of flexibility in different scenarios (such as tolerating a loss in %damage when you cubed with Hero's Gloves in mind, but ended up with Mu Gong's Gloves for the week).
This idea can be extended to a comparison of %stat and flat +stat boosts, and bonus cubes are a great way to provide these immediate and/or long term "fixes". In the end, if you want to optimize your character, you need to take a holistic approach; see what you have, recognize what you're lacking, and make a conscientious decision.
The relative values of potential lines are constantly changing (so long as you keep upgrading). Black cubes provide you the luxury of keeping existing potential, so you can always aim for an instantaneous %increase, no matter how small, without risk.
Whether the cost is worth it, however, is a different topic of discussion.