Changes in templates and other transcluded content often go unnoticed because often, specifically with templates, the transcluding page is added to the watchlist, but the transcluded page is not. This makes changes relevant to a transcluded pages escape the attention of interested parties. I'm not sure what the best technical solution is, hence the untechnical title of this issue, but a reasonable approach to me seems to be that when a user adds a page to their watchlist, all pages transcluded on that page are added to the users watchlist as well.

Another solution that seems less technically viable (but what do I know) is to display all changes to watched pages or pages transcluded in watched pages in the watchlist.