If you'd like to start measuring the size of your website's loyal audience, you can start by importing the Loyal Users Segment (3+ Sessions) into your Google Analytics account. Once you have this segment in place you can add it to any standard or custom Google Analytics report in order to understand how this group of users interacts with content or how they compare to other types of audience. For example, you can combine this with your goal reports to understand which activities loyal users are more or less likely to complete.
Keep in mind that this segment is a bit tricky to use. It applies the 3 session condition to the time period specified in your reports. For example, if you apply this to a report with a date range of one week, it will show only users who had 3+ sessions in that week. If you apply it to a year, it will show users who visited 3 or more times in the entire period. If you want to use this to pull monthly data, you must only pull one month of data at a time. If you wish to see a trend you will need to report each period as a separate report and consolidate the data in an external file or spreadsheet.