I've developed many Excel Applications during my career as an engineer in the power industry that work well in Excel because of the ability to do pre-processing of data, calculations, and post processing of data in a single app. If the intrinsic functions in Excel aren't enough it's easy to develop macros and/or link with other calculation or modeling engines. Microsoft will quit supporting Excel 2010 in October of this year. The applications I've developed use multiple excel workbooks and work poorly or not at all with a single document interface. If they work at all they are r-e-a-l-l-y s-l-o-w. The SDI interface in Excel 2013 and beyond is a disaster for me and it has really impaired my ability to provide excel based solutions to my clients. Is there a reasonable alternative? Will MS implement an MDI interface sometime in the future?
There's been much discussion on this site concerning this issue: