I did my last 90 days 15 days early.
Then I realized that I "lost" 15 days - it had become a 75days report, because the new 90 days started on the day of my report (but if you report late, during the 7 days grace period, the new 90 days start from the day you should have reported, not on the actual day of your report).
Result: the next 90 days report is due about 2 weeks before the next visa extension. So it will be 2 trips to CW insteaf of one..
Of course, I am always glad if I have a chance to visit CW.