In the section where you can insert calculated columns you can re-use previously used expressions. This is a handy feature. However, it shows all recent expressions. There is no option to include only the ones you want to be remembered. Hence Spotfire newbies often do not know which expression has worked for them the intended way. Ideally you are able to save a set of custom expressions in a central location in the library so all business users are making use of the companywide definition of a calculation.
And formats (Date time is a very important case in point )
The ability to store expressions in addition to other file types in the library is a critical feature. In my case, I need to store data files that are not in SBDF format to the library but I cannot. I suggest adding an API to register data files (with extensions) as 'savable' in the library.