It lacks setting up field-level security and adding fields to the page layout, so you have to choose the manual way of field creation. Adds another layer of risk with changes in Schema Builder since it is deployed in real- time.
Salesforce Schema Builder is a powerful tool for visualizing and creating objects, fields, and relationships in Salesforce, but it has certain limitations when building custom objects.
* Option B (Fields and relationships can be created, but they will be unable to add the fields to the page layout from the canvas): In Schema Builder, while you can create new custom objects, fields, and relationships, you cannot directly add fields to the page layout from within the Schema Builder interface. After creating a field, you need to navigate to the Page Layout Editor to manually place the new field on the layout.
Schema Builder Overview
Option A: This is incorrect because you can perform multiple actions within Schema Builder without needing to click Save each time. Salesforce will save these changes when you click Save once at the end.
Option C: While relationships can be created in Schema Builder for both standard and custom objects, there is no requirement to use Lightning Object Manager to create relationships with standard objects.
Option D: Schema Builder supports the creation of formula fields along with other types of fields. There is no exclusion for formula fields.
In summary, Option B is the correct limitation of Schema Builder: you cannot add fields to page layouts directly from the Schema Builder interface.
Reference:Schema Builder Limitations