I wish I had a dollar for every time I heard this claim. The truth is gutter guard can prevent some of the larger debris from entering the gutter, but that debris will still build up on roof area, along valleys and on top of the gutter guard itself.
This vegetation will still create a fire hazard in the bushfire season and will still rot down during wet times corroding your roof and your expensive gutter guard. Installing gutter guard does not prevent the need for maintenance to be carried out on your roof.
Broken down leaf matter, dust, bird droppings, seeds, pollen and contaminates can still get through the mesh in gutter guard and block your gutters. This can still form the perfect breading area for insects, mould, moss and vermin this lush compost then provides the ideal location for seed germination (Under your gutter guard).
Then how do you clean you gutters?
The removal of gutter guard to clean under it can be an expensive operation.
Seek some advice (Not from the gutter guard sales guy) before spending big dollars on gutter guard it may not suit your needs.
These photos taken in Buderim show a 12 month old home with good quality gutter guard, you can see the garden growing on the roof and the damage done to this modern home after vegetation and rotting matter was removed.