Optical modules are hot swappable, and you do not need to power off the device when replacing optical modules. The argument to this objection is simple: A correctly wired fixture will see. Small Form-factor Pluggable modules (SFP module) are the workhorses of modern network connectivity, enabling flexible fiber optic or copper links between switches, routers, firewalls, and servers. Whether you're upgrading bandwidth, replacing a faulty unit, or reconfiguring your topology, knowing. However, to answer the OP's question, I would say that extremely few people switch off the circuit when they change a lamp/bulb, and virtually none would switch off the entire installation. Turning off the switch effectively isolates the supply to the bulb I don't even turn off the switch.