Metric Categories are best used for challenges, onboarding or intaking client measurements, or if you have a lot of metrics.
Metric Categories are created under the metrics tab.
You can create the metrics or the category first. Once you have a category with metrics you can use it to filter inside the client account to make bulk uploading easier. To filter, you will just click the collection tag on the metric and it will show you only the collection of metrics you selected then select +Update All to Bulk Add the values.