XCode Edit Project Settings vs Edit Active Target

Project settings apply to all targets in your project. Target settings apply only to that specific target. You likely have only a single target which can make the two sets of settings confusing and appear redundant.

If a setting is set (appears in bold) for both the project and a target, the target setting overrides the project setting.

Target settings which aren't set (do not appear in bold) are inherited from the project settings. Project settings which aren't set (do not appear in bold) are inherited from Xcode's default settings.

If a setting (either project or target) is set (appears in bold) and you instead want to inherit that setting, select the setting and press Delete.

I suggest you prefer using the target settings. Use the project settings for larger, multi-target projects where you really do want to share settings across targets.

It's worth adding that properties set at project level are not automatically inherited from the different configurations / targets of your project: in order to inherit properties that are set at project level you need to set the value $(inherited) in the fields where you actually want to inherit such properties.