Benefits of Oil Primer
Provides an excellent bond for sealing over many layers or paint.
Better for older wood such as cedar which can hide imperfections.
Excellent for priming walls after wallpaper is removed. Glue stains will likely be apparent and oil primer will help to cover these stains.
Excellent for sealing nail heads and covering knots in bare wood.
Oil primer takes a bit longer to dry but will be worth it once the finish coat is applied.