I was pleased to see this entry in the latest Office 365 release notes.
Release notes for Current Channel wrote: Excel
- Reducing unwanted fragmenting of conditional formatting rules: Check out the speed up in workbooks with lots of unwanted fragmented conditional formatting rules. When a workbook is opened this feature will merge those fragmented conditional formatting rules that are identical, within a contiguous range of cells, and with unchanged priority ordering. It excludes rules whose evaluation relies on a selection range like Above or Below average, Unique or Duplicate, Gradients, etc. and rules in PivotTables.