The notifyUsers parameter was added to REST calls that update issues back in Jira 7.2.0, however, this parameter is not available for the '/rest/issue/{issueIdOrKey}/comment' endpoint.

Reference: Add comment

 
This feature would be useful for the same reason it's useful for updating issues. Under certain use cases, comments need to be added without notifying all users associated with the issue.

Another example comment-related actions that can't suppress notification:

curl --request PUT \
--url 'http://serverName/rest/api/2/issue/<issue-id>?notifyUsers=false' \
--user 'user:pass' \
--header 'Accept: application/json' \
--header 'Content-Type: application/json' \
--data '{
"update": {
"comment": [
  {
    "edit":{
        "id":<comment-id>,
        "body":"new comment body"}
  }]}}'