Mermaid diagrams are even better because you don't waste characters on the visual representation but rather the relationships between them. It's the difference between

    graph TD
            User -->|Enters Credentials| Frontend[React App]
            Frontend -->|POST /auth| API[NodeJS Service]
            API -->|Query| DB[(PostgreSQL)]
            API --x|Invalid| Frontend
            DB -->|User Object| API
            API -->|JWT| Frontend

and

    +-------+           +-------------+           +---------+
    |  User |           | React App   |           | NodeJS  |
    +-------+           +-------------+           +---------+
        |                      |                       |
        |  Enters Creds        |       POST /auth      |
        |--------------------->|---------------------->|
        |                      |                       |
        |      Invalid         |    <-- [X] Error -----|
        |<---------------------|                       |
        |                      |       Query DB        |
        |                      |---------------------->| [ DB ]

Plus while an LLM can understand relationships via pure ASCII or an image, it's just easier to give it the relationship data directly.