Why is RetentionHoldEnabled set to true during hybrid migration?

I noticed that my retention policies weren't being applied after migrating from Exchange 2010 to Office 365. I found this article indicating RetentionHoldEnabled is set to true during the migration and it needs to be disabled for your retention policies to function. What is the reason for this? Is there any issue with disabling this on all of the migrated mailboxes?

https://support.microsoft.com/en-us/help/3194755/retention-policy-no-longer-works-after-a-mailbox-is-moved-from-the-on