Updated: Dec 28, 2020
There is a continued and probably eternal debate about control arms (aka "a-arms") and how long they should be for any given application. The upper control arm is one of the things that determines wheel travel, suspension durability, and wheel alignment.
If you're making any sort of suspension modification at all, replacing the upper control arms should be considered.
Why Replace A Control Arm?
The most common reason to replace a control arm is to improve wheel travel as part of a suspension lift. However, a new control arm can offer more than just increased ride height (lift) and additional wheel travel:
Increased durability in the arm itself
A wider range of uniball/ball joint options
More compatibility with replacement coilovers
Many quality suspension kits for off-road vehicles include a control arm that hits all of these notes - more ride height, more travel, more durability, and better quality ball joints.
Additionally, wheel alignment is better compared to vehicles that use some sort of spacer to achieve lift.