Application developers configure ServiceNow using industry standard JavaScript to extend and add functionality. JavaScript is a scripting language that enables developers to create dynamic and interactive web pages, as well as manipulate data and logic on the server-side. ServiceNow provides various APIs and frameworks for developers to use JavaScript to customize and enhance the functionality of their applications, such as client scripts, UI policies, business rules, script includes, UI actions, and more. Reference: [ServiceNow Docs - JavaScript in ServiceNow], [ServiceNow Docs - Scripting in ServiceNow]

Administrators can grant non-admin users the ability to develop global applications. Delegated Development is for the scoped applications only

https://docs.servicenow.com/bundle/rome-application-development/page/build/applications/concept
/c_DefaultDesignAccessPermissions.html
The baseline behavior of a table in a privately-scoped application is that all application scopes can read from the table. A privately-scoped application is an application that restricts write access to its tables and resources to scripts within the same scope. However, read access is allowed by default for all scopes, unless the administrator explicitly denies it using an Access Control rule. This allows for data sharing between different applications while maintaining data integrity and security. References: [Product Documentation | ServiceNow], [Advantages of Scoped Applications in ServiceNow]

ServiceNow tables commonly use table extension, where a child table inherits fields from a parent table.
When a field is defined on a parent table, that field is automatically available on all extended child tables.
Because of this inheritance model, deleting a field that originates from the parent table effectively removes it from every table that inherits it, which can appear as "the field was removed from multiple tables." That behavior is characteristic of an inherited field: it is not independently defined on each child table, so it does not exist as separate copies to delete individually. A reference field is simply a field type that points to another table and would not inherently remove itself from multiple tables when deleted. A custom field is typically created on a specific table; deleting it would usually impact only that table (unless that table is a parent and the field is inherited, which is precisely the inherited-field scenario). "Base system field" is not the right explanation for multi-table removal; the key cause is inheritance through table extension.