What is the Purpose of Deprecated Code?

Question

I was changing out some PHP code the other day because it was deprecated, and no longer worked. I understand the meaning of deprecated code based on an answer I found here: https://stackoverflow.com/a/8111799/1810777

But several question came to mind:

1. I was wondering what is the purpose of deprecating code?
2. Why not just leave it in use, instead of recommending others to use new alternatives?
3. Does it slow stuff down?

I couldn't find anywhere else online that talked about it. I'm just really wondering why code that used to work well, isn't useful anymore. Thanks!

Answer 1

It means that in a future release it's going to be removed.

This allows an API developer to give people time to migrate to the new version / method of doing whatever rather than just pulling the rug out from under them. Both the new and the old versions are available for a limited time.

As for why not leave it there forever ... because there's a new, better way to do it. You can't support legacy code forever (if you value your sanity and your budget). All support has a cost (be that tech support hours, bug fixes, regression testing, etc)