Why formatting rules become a size and speed problem
Conditional formatting is stored on the worksheet as conditionalFormatting blocks. Each block has an sqref, the list of ranges it covers, and one or more cfRule children. A single rule over A1:A500 is cheap. The same visual result applied by a macro one row at a time becomes hundreds of rules, each with its own range. The styles part then carries a dxf, a differential format, for the colors and borders those rules use. Calculation slows because Excel reevaluates the rules, and the file grows because the XML lists every fragment.
What the checker counts
For each sheet it counts blocks, rules, and the number of ranges inside sqref attributes. A sheet is marked fragmented when it has more than thirty separate ranges, or more than ten ranges and more ranges than rules. The page also reads the dxf count from xl/styles.xml. That count is workbook-wide: it includes differential formats used by tables and pivots, so it is context, not a count of colors you typed.
The repair steps live in the guide on how formatting rules affect calculation.
How fragmentation happens
People copy a formatted cell down a column with a tool that duplicates the rule instead of extending it. They format a table, convert it to a range, and leave the rules behind. They record a macro that paints every cell matching a condition. None of this shows up as a formula you can find with Go To Special. It shows up here, as a rule count that looks absurd next to the size of the sheet. The fix in Excel is to open Conditional Formatting, Manage Rules, and delete duplicates, then recreate one rule for the whole column or the whole table.
How this relates to calculation
Formatting is not a volatile function, but a sheet with thousands of formula-based rules recalculates those formulas whenever the workbook calculates. Whole-column rules are especially expensive. If this page shows a high rule count and the volatile check also lights up, fix the volatile formulas first only if they are the larger number. Otherwise consolidate formatting before you rewrite ordinary SUM formulas. The Audit score deducts from file efficiency when rules pass 50, and more sharply past 500 rules or 200 ranges.
What the checker does not decide
It does not tell you which rule is the one your manager wants to keep. Two rules can be legitimate. The report is a count and a fragmentation flag so you can open Manage Rules with a number in mind. On .xlsb files, rules live in the binary sheet and are not counted. The page says so instead of reporting a false zero as a clean result. If you only have the binary file, save a copy as .xlsx when policy allows, then run the count on that copy.