This is a very good practice! We use it all the time as it promotes consistency and reuse so everybody uses same definition of "sales goal" or "start date" etc. And they don't have to type it over and over again.
You might also provide "building blocks" instead (or along) whole calculations to encourage people to make their own discoveries (and better calcs).
I think our Server admins have a habit of examining workbooks for most common datasources and bringing in repeating and "interesting" calculations.
Of course, this will put some additional strain to your extracts (and their refresh jobs) since Tableau materializes most of calculations in the extracts so maybe don't go too crazy. I once saw 600 column datasource in our repository - a bit too much for my taste
Thank you Dimtry for the response. I', glad to hear we are on the right track.