Windows users now have just 10 days to roll back updates, which is down from the 30 they were previously given. This change has been applied with the Windows 10 Anniversary Update. Once those 10 days are up, the Windows.old folder will be cleared, potentially opening up gigabytes of space.
Microsoft doesn't believe this will have a notable negative effect on users. Most people roll back within a few days, says Microsoft, so setting the limit to 10 days shouldn't be an issue.
Based on our user research, we noticed most users who choose to go back to a previous version of Windows do it within the first several days. As such, we changed the setting to 10 days to free storage space used by previous copies. - Microsoft