I'm going to assume you're referring to this feature of Salesforce:
With Organization Sync, you can set up a secondary, synced Salesforce organization which users can access whenever your primary organization is experiencing downtime or maintenance.
Ultimately, it comes down to making a business decision on whether you're getting an adequate return on your investment to justify the added expense and overhead to support maintaining a 2nd org in order to have the convenience of being able to switch over to a 2nd org during Salesforce downtime or outages. Clearly, there's a lot of additional admin and developer support required to maintain a second org. You need to be willing to test and maintain it to assure you can use it when needed.
Sync to a Secondary Organization has a number of limitations. These limitations need to be taken into consideration before deciding whether this a option you to seriously consider. Some of those limitations are things like the following:
- To use Organization Sync, you must purchase a secondary Salesforce org and its accompanying user licenses.
- The primary and secondary orgs must be the same organization type (for example, production or sandbox) and edition.
- To avoid inconsistent behavior, both orgs must have the same limits and settings. If the limits of the primary org have been adjusted, contact Salesforce to have the same changes made in the secondary org.
- To avoid Duplicates Detected errors, Salesforce recommends turning off duplicate management in secondary orgs.
Note: Organization Sync is designed to support a two-org setup but can be configured to work for more than two orgs.
Unsupported Objects and Features
- Auto-numbered fields aren’t synced, but you can implement a workaround.
- If you’ve enabled the option to sync feeds and audit fields, audit fields don’t appear in the list of publishable fields because they’re automatically synced. Audit fields are only synced when a record is copied from one org to another (for example, during a bulk sync). If an audit field on a synced record is updated, that update is not reflected in the linked org.
- Rich text area (RTA) fields aren’t synced.
- Formula fields and roll-up summary fields can’t be published because their values are determined by other fields’ values (There's a workaround that needs to be implemented in the secondary organization).
- Lookup fields to unpublished objects aren’t automatically published because publishing such fields can cause syncing errors.
- Callout fields such as geolocation fields aren’t synced.
- Only certain objects can be published in Organization Sync. For a list, see Which Objects Can Be Published?.
- Certain types of metadata aren’t supported. For a list, see Which Types of Metadata Are Synced?.
- Supported metadata is only synced in one direction, from the primary to the secondary org.
- LiveAgent, Salesforce Knowledge, Portals, and Communities aren’t supported.
- Managed packages aren’t synced. If you wish, you can install a package on both organizations to keep the user experience consistent.
- Chatter file posts larger than 2 GB aren’t synced.
- Chatter topics, groups, and likes aren’t synced.
- In synced Chatter posts, user mentions aren’t clickable.
- Chatter file versions aren’t supported.
Automation and Data Structure
- Multi-level lookups with more than one level are only synced during bulk syncs.
- Apex triggers, processes, and workflows aren’t duplicated from one org to the other because duplicate automation can lead to looping updates or errors. You'll need to adapt your existing triggers, processes, and workflows for the secondary org.
- Users are only synced in one direction, from the primary to the secondary org.
- A bulk sync can only copy records that were last created or modified no more than one year before the bulk sync date.
- If the secondary org contained records before you established a connection between the two orgs, those pre-existing records in the secondary org aren’t auto-connected to matching records in the primary org.
- Salesforce does not recommend using a two-way sync for some objects and fields and a one-way sync for others.