Gen4 controllers consume more power than Gen3. Revision 4.0 updates the M.2 power management sequence to support with lower exit latency.
For the most common M.2 configuration—the x4 slot used by NVMe SSDs—the implications are profound: Pci Express M.2 Specification Revision 4.0 Version 1.0 Pdf
The primary distinction between the Revision 4.0 and its predecessor lies in speed and efficiency. PCIe M.2 Rev 3.0 PCIe M.2 Rev 4.0 Bandwidth (x4 Lane) Real-World Read Speed Up to 3.5 GB/s Over 7.0 GB/s Compatibility Backward compatible Fully backward/forward compatible Industry Impact and Market Availability Gen4 controllers consume more power than Gen3
Drastically reduced render times for 4K and 8K video editing. Pci Express M.2 Specification Revision 4.0 Version 1.0 Pdf