Why is my bill more (or less) than usual this month?

Because of month in advance billing, if you make changes to your subscription the first bill will be prorated. If you've added services, the first bill is higher. If you've removed services, the first bill will be lower.

Example:
July 1st you bill for Essentials for the month of August.
July 20th you upgrade to Enhanced.

On your August 1st bill, you'll be charged for the difference between Essentials and Enhanced for July 20 - Aug 31, plus your new month in advance charges.