A really common problem which we often get called about is that after a relatively short number of years peoples cushions start to sag in an area and they lean into the middle of the sofa. It gives you back ache and is very uncomfortable.
You can see from the image below how the middle of the cushion is sagging .
We have replaced the foam in this suite and used a technique to try to reduce it from happening so quickly again in the future. We also use a better grade foam which again should help with the problem.
The sofa is put back together and you can see the seat is again flat, although the leather has stretched in the area. The sofa is returned with instructions to try to move around and use all the area of the foam to encourage even wear as you can not turn and swap cushions around on this style of suite.