Key vault access policy confusing note

In the documentation of key vault and key vault access policy resource is this note.

https://registry.terraform.io/providers/hashicorp/azurerm/latest/docs/resources/key_vault
https://registry.terraform.io/providers/hashicorp/azurerm/latest/docs/resources/key_vault_access_policy

It’s possible to define Key Vault Access Policies both within the azurerm_key_vault resource via the access_policy block and by using the azurerm_key_vault_access_policy resource. However it’s not possible to use both methods to manage Access Policies within a KeyVault, since there’ll be conflicts.

The bold sentence is confusing. I can use both methods (assumingly for managing access policies in key vault) but also it’s not possible to use both methods to manage access policies within a key vault?

So can I use both resources at the same time or not? In which case are there going to be conflicts?