This type of belt prevents a slumped seating position. And yes, if you stay on the bike long enough, you too will suffer from this.
Those who already have back problems, or who prefer not getting them, can choose for more comfort and stability with these kidney belts. There are different versions - always to be worn underneath your motorcycle jacket, but above first-layer clothing - which have a number of specific properties.
You have ventilated versions for warm weather and padded ones for cold, just like there are the ones with a double buckle which you can tighten thanks to two extra elastic bands.