Your active users can be found in last months 'Total Time' drill down in the Practice Performance report. The number of unique names is the number of active timesheeting users for that month.
This number changes each month and if you're on a monthly plan, your pricing will update both up and down to as you move between the pricing brackets found at www.linkhq.com
If you're on an annual plan (and benefiting from the 20% annual discount), your active timesheeting users are only measured on your annual renewal date, so any changes up or down will not change your pricing.
Because not all of your XPM users do timesheets, some of your XPM users will not be counted toward your active users for any Link products so there is no financial benefit to remove inactive users from your XPM (because we're already not counting them).