Draft environments by definition are complex beasts, with an interconnected variety of different factors affecting the design’s dynamics. Each card included will subtly (or not so subtly) shift the balance of your environment. Designers must consider the interplay effects like removal, mana fixing, aggression, acceleration, and control, to name a few.
When thinking about balancing these different concepts, the analogy I like to use is a sound mixing board. 
When creating a piece of music, the goal is not to slide all the dials as high as they can go, but to mix the components in the way that is most pleasing to the ear. If you move all the sliders to 10, you may find that the bass completely drowns out the vocals, and that the sound produced is not very cohesive or well balanced.
Similarly, in cube design, many beginning designers first instinct is to shove all the archetypes power levels to their proverbial maximum. Unsurprisingly, this method of pushing everything to “10” tends to result in environments that aren’t very well balanced at all. And why should it? Wizards has printed cards for over 20 years, and never did so with an eye towards ensuring that a power maximized selection of cards from the game’s history would produce a satisfying draft environment. A quick look at something like the Legacy Constructed Banned List confirms this. Wizards has printed dozens of game-breaking and unfair cards over the years, but not a single one of those cards was banned due to its efficiency as an attacking creatures.
If you scour various cube article archives, you’ll inevitably find one that implores the reader to “support aggro”. This stems from the fact that when selecting the best of the best from Magic’s card pool, aggro often doesn’t stack up well against other archetypes. Aggro’s “10” is seldom as powerful as control or combo’s “10”. Luckily, the fix is rather straightforward, albeit not necessarily easy.
Let’s return to our soundboard analogy. If your song’s vocals were being drowned out by the bass, and both are already pushed to 10, what are your options? Slide down the base, or find some way to slide your vocals past “10”, or some combination of the two.
For now, we’ll focus on proverbially “sliding down the bass”. In Cube terms, most often this means trimming down on your oppressive anti-aggro cards. Justin Parnell wrote a great article on supporting aggro, wherein he identifies common cube cards that can make it difficult for aggressive decks to thrive in an environment.
Cube design doesn’t require cutting all of these necessarily, but trimming oppressive cards is one of many tools for balancing an environment in a cube designer’s arsenal.
Taking things one step further, Christopher Morris-Lent compiled a list of Magic’s eight most oppressive cube cards.
There are infinite ways to balance a cube, and cube design is all about finding the mix of cards and effects that is most appealing to you and your drafters.