This is a general warning message as Pega wants to encourage use of Data transform and other rules before one chooses writing an activity. So you can just provide the justification stating the purpose for which you need the activity.

You can reduce the number of activities that are required in some cases. This link might help you.

https://pdn.pega.com/java-and-activities/nine-tactics-to-reduce-your-need-for-custom-activities-prpc-62-sp2

Thanks,

Ashok

If you are using for property-set try to use data transform and to remove the severity level for that activity include log-message method.

Whenever you create an activty, make the activity type as utility. Then u wont see any warning messages.