When a master item is in use and you click edit you do of course see a warning message that the changes will impact all instances. Helpful - yes / no ?
As Qlik Sense has already identified this, can we open up the warning to advise the user exactly in which objects the master item is used - to help them focus their minds on the impact of the change.
Even if the item is used in a huge number of places a mini-list would better than the current alert.
Or ideally, go a stage further and provide a mechanism in the assets panel so that a user can see a complete sheet -> object reference list for all master items - maybe as an extra tab inside the master item edit pane.
Analogy = you are a librarian. Do you lend your books without knowing who is using them - no. And you always have access to that list to see where they are at any moment in time.
Please change Qlik Sense master items into a more user friendly library. In many organisations it is a valuable corporate asset for analytics.