Energy loss
Even a small unwrapped section of a hot pipe can lose significant energy continuously. Across a year, the cost of leaving it adds up quickly.
Condensation and corrosion
On cold pipework, a damaged vapour barrier lets warm air contact the cold surface, condense, and run down inside the insulation. That water accelerates corrosion on the pipe — and stays hidden until something fails.
Maintenance access
If insulation has been cut open repeatedly for maintenance, it's usually cheaper to replace damaged sections with removable jackets at known access points than to keep patching.