Backwards compatibility is important when it comes to looking at new systems and services. It can be costly to replace existing applications or convert working and historic data.
If you are looking to make a wholesale change to some of the fundamental services that your company works with make sure you include the soft costs in your analysis.
Every company large or small will have amassed a level of knowledge of internal working practices and procedures over the lifetime of the systems that will need to be relearned should the system be replaced. This reduces productivity, increases the number of errors and the support overhead alongside the cost of making the change.