Among other things yEd is great at analysis of something in graphical form. If you can put a thing into an Excel file, you probably can load it into yEd as a graph and then visualise using plenty of layout tools, e.g. using hierarchical layout for topological sorting and finding a critical path.
With that regard, sometimes it necessary to overlay information taken from multiple sources onto the same diagram. For example, taking list of nodes from file A and taking list of edges from files B and C. Right now I need to put everything into the same file, but would be good to be able to incrementaly import more and more nodes and edges from additional files into the same diagram