By default whenever you create an activity its Usage type will be Activity which gives the below warning to users,
The use of activity rules should be limited. The need for activities can be reduced by using data transforms, as well as techniques such as case management, the Engine API, and declaratives.
This warning is provided to developers inorder to reduce the need of activites and try to achieve there requirement using data transforms.
Suggestion: You just can't change the activity usage to Utility until it really fits to be an Utility. Kindly check the documentation of Activities for better understanding before converting to Utility.