I've had a request for a mains conditioning unit on a system that has run off mains for years with no problems. I've never heard of any surges or oddities like that and so I'm wondering what the value of mains conditioning in protecting equipment really is.
It isn't just about protecting equipment, it is about the requirement of consistent power to get good quality sound. Lots of processing in sound is based around relation to a standard power level to determine how strong a signal is. If you don't have well conditioned power, that level can change... a LOT!!! Particularly if it is fluctuating greatly you can end up with significant changes to how a sound is processed by equipment and result in unpredictable results and/or excess noise floors.
There is also always the possibility that a major surge could damage gear, but that's not the main concern at all. Major surges are a very rare occurrence, though they can occur and be devastating to gear, but their rarity really makes them not the primary concern. Sound quality and predictable, level power is.