I take it you run cannisters of some sort on your systems? One of the downsides of cannisters, compared to sumps (yes, I run sumps) is that you only have 'x' amount of space for mech, and 'x' amount of space for bio. You are stuck with those limited spaces.
All too often, due to this limited space, I think most people find that their bio section alone isn't always up to scratch on producing enough BB for their bio load. And so they begin to rely on BB within the mech side too.
This can be a problem when maintanance time comes. Usually you'd leave the bio media alone but when washing/rinsing the mech side how vigorously, and for how long do you rinse it when you're in danger of getting rid of a heap of BB too?
Wash too much and you might get a spike in ammonia for a while when you put it all back together. Wash too little and you've still got a load of crud in your filters.
Also, although it is the correct and recognised thing to do, you must always wash your mech filters in a bucket of tank water. But once you start squeezing those sponges....ugghhh, the water goes muddy and then the whole point of cleaning/rinsing has completely gone!
My mech side gets blasted under the tap. Hot, chlorine rich tap water, and whether any BB get annihilated along the way, it doesn't matter, because my large bio sections are more than capable of coping. Never do I experience parameter spikes after filter cleaning.
If I ran cannisters I think I'd run sponge filters in conjunction too. Hopefully there'd be enough BB in the sponge filter to cope with any BB losses in my main filter during cleaning. That way you too may also get away with blitzing your mech side under "deadly" hot tap water.
I do the same exact thing. Rinse my mechanical filtration in hot tap water, but I also run a sump that is half the size of my tank with more than enough bio media to cope with it. I don't ever get spikes either.