I store my undertray behind the shed, that way I'm alerted to any impending leaks from places they shouldn't, I don't get advisories at MOT time in relation to obscured components, and it makes changing the oil easier.
Other advantages include, no hidey holes for stuff you drop, and it's much less likely to cause a problem if you encounter high "speed cushions" in the road.
Complete waste of time, unless you think........ **
1 I will get 100MPG with this aerodynamic component fitted to the underside of the car
2 As above, but the car will be much faster to accelerate away from the lights.
3 It will prevent my engine bay becoming soiled with road spray
4 I can complain if the garage fail to refit it, because the original fixings have long since disappeared and been replaced with 8,000,000 cheap cable ties from the pound shop
Of course being stored behind the shed, it won't be stolen by Halfords in Birmingham either
Lovely
Brian