So, if you, somehow, have managed to get your back part (housing) damaged. Damages of the housing may include:

• Deformation of the housing
• Housing breaking into pieces
• Visible scratches and dent
• The housing of the iPhone 6s Plus bent, stressed
• Loosening of the adhesive that holds the housing

Any sort of damage or deformation on the back housing of the iPhone 6s Plus indicates that it might lead to an internal issue in the future. Also, a damaged back housing may harm your inner part like the battery, display, and other peripherals of your iPhone. An iPhone 6s Plus is not IP68 rated. But it protects your phone from dirt and dust as much as it can. However, it can’t protect your phone from dust and water with damaged housing. And in that sense, the housing of the iPhone 6s Plus serves more purpose than just visual aesthetics.