What is a master detail relationship?
Keeping this in view, when should you use a lookup instead of a master detail relationship?
A typical use of a Master-Detail would be the classic Sales Order and Sales Order Items objects. Lookups are generally for use where you may or may need to have a relationship between two objects (but not always). Lookups are generally used to reference commonly shared data, such as reference data.
Keeping this in view, what is a lookup relationship?
A Lookup relationship involves finding value of a field based on the value in another field in another object. It is mostly used in the case of commonly shared data between two objects.
Instead we have to first create Look up fields then fill all the records with that lookup filed. After that we can convert the lookup fields to master – detail relationship. If we delete master records then detail (Child) records are deleted. It creates the parent(master) child(Detail) relationship between objects.