plain text has a lot to be said for it, in that if one tool somehow does not work there are a lot of possibilities for going back and using other tools or using textscan() or the like.
However, plain text does not handle hierarchies of data well, so you start to need structured text -- but then you start to become reliant on the tools that handle that structure.
Plain text is not the fastest. Note that xlsx files are plain text internally, so they are slower than binary files -- but have the advantage that there are a lot of tools to examine and process xlsx files.
Dates and times are a perpetual challenge, because people outputting them often ignore questions about whether the times were local according to "summer time" in effect, and if so what were the transition dates that year, and were leap seconds included, and what is the available time resolution, and what timezone are the in, and what is the base of the calendar (e.g., georgian vs gregorian), and whether the times are Earth based or solar times, and so on. The time needs for GPS purposes are not the same as ordinary human times...