If you look at a carving knife set, whether it be Xacto or something else, you will see many different blade shapes. There's a blade with a lot of belly, a hawkbill, a triangle-shaped blade (like the front part of a tanto), a straight blade (like the back half of a tanto), and several other blade shapes. If you look at the currently available offering of production knived, you will see similar variation. Different blade shapes excel at different types of tasks. I don't carry a tanto, but I probably will in the future (in addition to at least two other knives). I will carry one because I can use the tip to puncture hard materials without worrying about the tip chipping and because I find the front edge useful for scraping things. IMO, the tanto, like the hawkbill, isn't the most useful all-around blade shape, but in addition to other knives it can give a wide variety of options. Use what works for you - if you find tantos useless, you probably don't need one.
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Jason aka medusaoblongata
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"Is not giving a need? Is not receiving mercy?" - Thus Spoke Zarathustra
"Cutting his throat is only a momentary pleasure and is bound to get you talked about." - Lazarus Long
"Knowledge is not made for understanding; it is made for cutting." - Michel Foucault