Hi Siqing Zheng,
Adding to @akinbade abiola
The main advantage of using a single managed identity for all subscriptions is that it simplifies management and reduces the number of identities that need to be created and managed. This can be especially useful if you have a large number of subscriptions or if you frequently create and delete subscriptions.
On the other hand, using a user-assigned managed identity for each subscription provides more granular control over access and can help to limit the blast radius in case of a security breach. Additionally, using separate identities can make it easier to track which identity is being used by which subscription.
Ultimately, the decision of whether to use a single managed identity or multiple user-assigned managed identities will depend on your specific requirements and security needs.
Hope this will help.
Thanks,
Shweta
Please remember to "Accept Answer" if answer helped you.