For LaTeX it is still of interest in special circumstances where one preloads classes and packages as well and then dumps the fmt file.
In a current project of mine, I was able to improve the format time of a document from 4 sec to 0.4 secs with usage of such a format file. It's not much for one document, but since (a) we're producing ca. 15 million documents a year and (b) this is also used in an interactive environment, such performance improvements were very well received by our users.