Whether a bob should be shorter at the back depends on personal preference and the specific bob style you desire. Classic bobs are generally the same length all around, offering a timeless and versatile look. However, graduated bobs have a slight stacking effect with the back shorter, providing volume to the crown. Inverted bobs are shorter in the back and longer in the front, offering a trendy and edgy appearance. Asymmetrical bobs have uneven lengths on each side, with one side shorter for a bold and modern look. Ultimately, the choice depends on your individual style, face shape, and the aesthetic you want to achieve. Consulting with a hairstylist can help you find the perfect bob style to suit your preferences.