By default, component properties and their values are saved with the project. Meaning that a property in a Perspective Session will initialize with a value matching the last saved value. This is why you can create a label with a static text value, save, and then see the same text value in the session. These properties are considered Persistent.
Conversely, properties can be configured to not retain their value in the session, meaning they'll initialize without a value. These properties are not Persistent . These properties are denoted by the Transient icon to the right of the property's value in the Property Editor.
Changing the Persistent state of a property can easily be accomplished by right-clicking on a property in the Property Editor, and toggling the Persistent option.
Persistence and User-Created Properties
User created properties missing the Persistent flag will not be saved in your project. Meaning, properties that are both user-created and not flagged as Persistent will be lost once the view containing the property is closed in the designer (not just the value, but the property itself), regardless of whether or not the project was saved. This is also true for launching a session, as the user created property that is not Persistent will not be present in the session.
The one exception to this rule is if a binding was configured on the property. Binding configurations are always saved along with the component, and will execute in the session. The existence of a binding on a property will result in the property being re-created in the session.
Bindings and Persistence
When configuring a binding on a property, the property will automatically be configured to not persist. The idea being that properties with bindings generally don't need to save their value along with the view: when a view is opened, all bindings will need to evaluate on startup, which means the last saved value on the property is likely to differ from the result of the binding.
Imagine a table component, with a binding on the table's data property. In most cases, you'll likely want the data in the table to be generated in the session from the binding, retrieving the most update-to-date results. In this case, it doesn't make sense to persist the dataset in the table along with the table, as it's just extra data that will quickly be replaced by the binding at runtime.
Bound properties default to a non-persistent configuration, but sometimes this isn't desirable. For example, Embedded View components have an empty state when their "path" property is blank. When a binding is placed on the path property, opening the parent view will result in the Embedded View quickly transitioning between the empty state and the loaded view, which can cause an undesirable "flash" as the binding evaluates. This can be prevented by configuring the property as Persistent, and configuring an initial path for the Embedded View (which can lead to an empty placeholder view), allowing for a controlled transition.