Grooming isn't strictly necessary unless you have an Angora rabbit whose coat can grow to around 5in/12cm long. Angoras will need at least 40mins of brushing and care every day, so choosing this breed is a decision that needs some serious thought.
Spending time with your rabbit
Rabbits love to be clean and will spend much of the day cleaning and preening themselves. Although not strictly necessary, grooming does provide a good opportunity for you and your rabbit to spend some quality time together. Every 3 months or so your rabbit will shed some of its fur alternating between a light and heavy shed. A good brush can help the loose fur to come out.
Washing your rabbit
It is unlikely that you will need to wash your rabbit. They are very good at grooming themselves and as long as their house and run are kept clean then you won't run into any problems.