Record types allow you to update the options in a picklist based on the kind of opportunity.

One scenario that could prevent an administrator from changing the relationship between work item and project custom objects from master-detail to lookup is that roll-up summary fields exist on the master object (project). Roll-up summary fields are fields that calculate values from related records in a master-detail relationship; they cannot be used in a lookup relationship. If roll-up summary fields exist on the project object, they would prevent the administrator from changing the relationship type unless they are deleted first. A junction object is not required to support a lookup relationship; it is only used when creating many-to-many relationships between two objects using two master-detail relationships. The lookup field in all the records containing a value or the lookup field being required for saving records are not scenarios that would prevent changing the relationship type; they are scenarios that would allow changing the relationship type without losing data or functionality. Reference: https://help.salesforce.com/s/articleView?id=sf.fields_about_roll_up_summary_fields.htm&type=5 https://help.salesforce.com/s/articleView?id=sf.relationships_considerations.htm&type=5

To require users to choose a specific search engine from a picklist when lead source is "Search Engine", and hide it otherwise, the administrator should create a picklist for specific search engine on the same screen as lead source, and set conditional visibility so that it is only shown when lead source is "Search Engine". This will make sure that users see only relevant fields based on their input. A decision element will create an extra screen that may disrupt user experience. An assignment element will not affect field visibility. A validation rule will not hide fields but only show errors when values are invalid. Reference: https://help.salesforce.com/s/articleView?id=sf.flow_ref_elements_screen_components_picklist.htm&type=5 https://help.salesforce.com/s/articleView?id=sf.flow_ref_elements_screen_components_conditional_visibility.htm&type=5

Report type is a tool that can be used to pull contact fields into the custom report for Event. Report type defines the set of records and fields available to a report based on the relationships between a primary object and its related objects. To edit the custom Event report type and add fields related via lookup, go to Setup > Report Types and select the Event report type. Then click Edit Layout and drag the fields from the Contact object to the layout. Reference: https://help.salesforce.com/s/articleView?id=sf.reports_builder_create_report_type.htm&type=5

Formula fields are types of fields that calculate a value based on an expression or formula that references other fields or constants. Formula fields prevent administrators from changing their field type once they are created because they may be referenced by other functionalities such as reports, validation rules, workflow rules, etc., that depend on their data type and value. If a formula field is referenced by other functionalities, then changing its field type may cause errors or unexpected results. Reference: https://help.salesforce.com/s/articleView?id=sf.fields_about_formulas.htm&type=5