The inclusion of a bo-hi, also known as a fuller, on a katana blade is a matter of personal preference and depends on the intended use and purpose of the sword. Here are some aspects to consider when evaluating the benefits of a bo-hi on a katana:

1. Weight Reduction: The primary purpose of a bo-hi is to reduce the weight of the blade while maintaining its structural integrity. The fuller is a groove that runs along the blade's surface, creating a hollow section. This reduces the overall weight of the katana, making it more maneuverable and easier to handle.
2. Aesthetics: A bo-hi can enhance the visual appearance of a katana. The grooves add a distinctive design element to the blade, contributing to its overall aesthetic appeal.
3. Sound and Vibrations: The bo-hi can alter the acoustics and vibrations of the blade when it cuts through the air or strikes a target. Some people enjoy the sound and feel produced by a katana with a bo-hi during sword movements, considering it a unique aspect of the sword's character.
4. Potential Strength Reduction: Adding a bo-hi involves removing material from the blade, which may result in a slight reduction in strength compared to a solid, ungrooved blade. However, if the bo-hi is properly executed and doesn't compromise the structural integrity of the blade, the reduction in strength is typically negligible.

It's important to note that the presence or absence of a bo-hi does not necessarily make a katana better or worse. It is a matter of personal preference and intended use. Some practitioners prefer katanas with bo-hi for their weight reduction and aesthetic appeal, while others prefer solid blades for their perceived increased durability.

Ultimately, the decision to have a bo-hi on a katana should consider factors such as the user's preferences, intended use (e.g., martial arts practice, display, or cutting exercises), and the craftsmanship and quality of the specific katana in question.