App Data or Page Data Variables vs Retrieving

What’s the advantage of creating a variable in App Data or Page Data that’s called isValidUserSession if it’s easy enough to call the block "Is Valid User Session? Examples below. I noticed this behavior in a blueprint template app and I’m wondering why the style is this way.

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Hi.
The difference is the block makes a call to the server.
If you need such a value in several places it is better to store it in the variable.