I'd say it has a lot to do with how your app/platform is used along with use cases for your platform.
If you're snapchat and you promise people that you delete customer images after 15 seconds then you sure as hell better delete them.
However if you are Trello and you delete a task, I can see a reason for doing a "soft delete" and allow a customer to recover their task in-case it was an accident. They actually offer an "archive" option first before a hard delete. Now I can imagine even if the hard delete happened that maybe Trello still doesn't delete the task and not jeopardize their business.
If I decide to keep the data, it would depend on me figuring out few things such as:
1) how likely it is the user comes back for that data?
2) are there analytics which I can run on this data?
3) is the cost of storing this data more than the value if its lost?