Having a revolving field in an alternator offers several advantages, including:

1. Ease of construction: A revolving field is easier to construct and assemble compared to a stationary field. The construction of a stationary field requires more complex arrangements of poles and windings.

2. Better insulation to the armature: A revolving field allows for better insulation of the armature winding because the armature is stationary and can be easily insulated from the rotating field.

3. Reduced rotor weight: A revolving field eliminates the need for slip rings and brushes which are used to supply DC current to the rotor winding in a stationary field alternator. This reduces the weight of the rotor, making the alternator more efficient and less expensive to manufacture.

Overall, the use of a revolving field in an alternator offers several advantages in terms of ease of construction, better insulation, and reduced rotor weight, making it a popular choice for many applications.