Adobe Illustrator CS (ending with CS6 in 2012) operated on a perpetual licensing model. You walked into a store (or downloaded the installer), paid a one-time hefty fee (often upwards of $600 for a single app), and you owned that software forever. You could install it on your machine, and as long as your hardware supported it, it would run. If you wanted the next version (CS7), you had to pay for an upgrade.
The "Simplify" tool in CC is
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The most significant difference between Illustrator CS and Illustrator CC has nothing to do with vectors or bezier curves—it has to do with ownership. Adobe Illustrator CS (ending with CS6 in 2012)
Introduced in CC, Puppet Warp allows you to take a vector character or object and pose it naturally by placing pins on joints. In CS, posing a character meant rotating individual limbs layer-by-layer, often resulting in broken joints that required manual patching. If you wanted the next version (CS7), you
CS6 only had linear and radial gradients. CC introduces (points and lines) – think of painting with color stops anywhere on an object.
If you rely on plugins for prepress (e.g., Esko, CADtools, Phantasm), CS6 is a dead end.