When programming, I take some care regarding updating of external dependencies, to be sure that my code isn't affected. With LaTeX (I'm using MikTeX), it seems harder to know when I should update packages. In programming, my big concern is the possibility for errors or interface changes. With LaTeX packages, this is a concern, but it seems it's also possible for documents compiled with one version of a package to look quite different when compiled with a changed version. Separately, I've asked a different question regarding automatic regression testing of compiled documents.
How should one know when to update and whether the update is worthwhile? If it helps, I'm focusing on using MikTeX and CTAN.
Note 1: This question differs from this one as I am focused more on the practices of updating, rather than the setup of MikTeX.
This question is interesting regarding keeping informed about obsolete and recommended alternative packages, but differs because I am focused issues that affect many files, rather than just thinking about how to better use a given package. Some older files don't necessarily need to be reworked (e.g. things that have been published).