Most would agree that dirty, dusty equipment looks bad. For some equipment, it also affects the performance and lifespan. Audio amplifiers with dust-covered vents can overheat and shut down and/or have their lifespan reduced by operating at higher temperatures since the cooling fan can’t keep the unit cool. This applies to any equipment with vents and cooling fans (including computers). The filters on video projectors can get clogged and hinder airflow as well, causing the lamp(s) to operate at higher temperatures than they should, decreasing their lifespan. In some cases it can damage other parts of the projector as well. Lighting dimmers and dimmer racks should also be cleaned to ensure proper airflow.
The instruction manuals that come with equipment should contain maintenance information; be sure you’re familiar with the required maintenance of all your equipment to ensure it will continue to perform properly and will last a long time.