If you reach a level of project maturity where you don't have (or want to have) the entire db model in your head you should use it.
If you have multiple models in different systems you should use it.
If you work with other people and you want to make it easier to communicate db models you should use it.
If you want to communicate db models publicly you should use it.
If you want to plan your db models in advance you should use it.
When I say you should use it I mean the end diagrams, I don't specifically mean this tool.
If you reach a level of project maturity where you don't have (or want to have) the entire db model in your head you should use it.
If you have multiple models in different systems you should use it.
If you work with other people and you want to make it easier to communicate db models you should use it.
If you want to communicate db models publicly you should use it.
If you want to plan your db models in advance you should use it.
When I say you should use it I mean the end diagrams, I don't specifically mean this tool.