I just lost half an hour because a custom resource pattern was dropped from the compiler options when someone else checked in his .ipr that didn't have this setting.
Can you restore your version from source control?
Storing project files in VCS is warranted by that issue. It makes it easy for new developers to check out and work right away, rather than asking around for how to set up the projects.
The workstation development environment configuration is vital for the team. It's not a deliverable, but it affects the team, for better or worse. Having a standard development environment ensures that you are all working as similarly as possible rather than everyone having the projects configured slightly differently, which could result in false errors.