Currently BIDS/SSDT saves a bunch of package metadata in the project file:
which means a great trouble when more than 1 developer works on the SSIS project.
Imagine following typical situation:
1. Developer1 checks out and starts working on an existing package1 => version information is updated in the .dtproj file
2. Developer2 checks out and starts working on an existing package2 => version information is updated in the .dtproj file. He adds, for instance, a new parameter to the package2
3. Developer2 checks in his changes + the changed .dtproj file
4. Developer1 now has the "pleasure" to merge his changes in the .dtproj file with the check in of Developer2 before Developer1 can actually check in his work