As fellow sword enthusiasts, practitioners, and collectors, we are always stuck with the same question when we first start to buy swords. Knowing myself, I have always not been satisfied with just one of something. I have to have different models and types of something. Whether it is swords, firearms, or even computers.
Munetoshi Hira Zukuri Performance Katana.
In my opinion, there are two main schools of thought regarding sword usage, and how many you should own. Some support the idea that you should have one sword that can do everything, or will satisfactorily do most things you need it to do. However, like almost all things in life, that will simply give you good performance in one aspect of sword usage while impairing you for others. I am of the opinion that specialized tools get the job done better. For soft, medium, and hard density targets, why not get the best sword for each category that will give you peak performance in their respective areas?
An example of a light target, a water bottle.
An example of a medium density target, tatami omote.
An example of hard density targets, bamboo.
For example, if we were to talk about Japanese style katana then you have those swords made for battle, and those made for dueling during peacetime. The most common trend for wartime swords is that they are heavier, thicker, wider, and more robust in order to handle extreme stress without breaking. These are the kinds of swords that you would expect to be able to cut through 4 inch bamboo easily. However, if swords were all made in one way, then we wouldn't have an evolution of sword form and shape. During peacetime where dueling was more common, Samurai required swords that they could handle with ease, have a thinner and sharper edge for unarmored opponents, and could be more ornamental.
Even in Europe, if all the knights and warriors wanted to do is slash at armored opponents, everyone would have been using great swords. But swords again evolved to tackle different tasks with different shapes. You have the wide blade of viking style swords which are good for slashing, or you can have long thin, very pointed swords that were good for stabbing with dull edges. Of course, one has to take what I'm saying with a grain of salt because sword evolution is directly tied with armor evolution, however there are always swords that become specialized for a task.
Examples of Viking swords.
Example of European Longsword.
In short, there is no "one sword that fits all tasks". From a physics standpoint, that is not even remotely possible. There is a reason as to why thin performance style blades cannot handle hard dense targets well and the opposite applies for thick armor-crushing swords. Let's pretend that two simple one-handed Viking style swords are made. One has a cross section near the tip that is only 2mm thin, and another has a cross section in the same area 4mm thick. Width, fuller, furniture, etc. are the same. So they differ in weight and thickness. The thinner performance style sword will do extremely well in cutting soft targets such as newspaper sheets, plastic bottles, and tatami mats because the thinner cross section means that it will disturb the target less as it passes through. Now the other sword won't be able to cut through soft targets with as much ease, it will wedge more through the targets and disturb it more as the sword passes through. However, which would you use on hard targets such as a wood shield or bamboo? Definitely the thicker sword for its stronger cross section.
So here is my point. While technically one sword can do most of what you want it to do, from cutting soft targets to hard targets, it will only excel in one category. This is why, for those who seek great performance from their swords in multiple target areas, the minimum type of swords you should own is three. One strictly for soft target cutting, one for medium targets, and another for thick, heavy targets.