How important is a lab system?

How important is it to have a lab replicating your production (VoIP)
environment?

Conventional wisdom says that everybody has a lab: some people just
host their production users on it.

Having a lab incurs a lot of additional cost and work:

— You have to buy the lab equipment, and the software.

— You have to install and integrate the lab system.

— You have to keep it up to date and secure.

— To use the lab, you have to do everything twice: first on the lab,
then once it's proven, on the production system.

It's often easier to buy the lab gear in the first place than it is to
do all the work to actually use the lab.