A more accurate description would be "blades for cutting heavy duty materials".
In an ideal world all plotters would have sufficient power to drive the type of blade that is suitable for cuting thick and tough materials but far too many do not because their owners chose them (or were sold them) on price rather than power.
Most of the affordable machines in common use were not designed to cut many of the increasing range of tough, thick and abrasive materials now being marketed to the sign industry.
Many people believe or have been misled to believe, that their plotter should be able to cut any material they want and anything their material supplier wants to sell them.
Far too often we hear "my material supplier said all I need is a 60 degree blade"
Far too often we ask "did your material supplier ask what machine you have?"
Far too often we ask "would you try to travel to the moon on a bicycle?"
Some thick and tough materials can be cut on some plotters but only if the plotter has the power to drive the correct type of blade that is suitable for cutting those materials.
COMPROMISES (but not miracles)
Sometimes, to make it possible to cut some tough materials on plotters with limited power we make some blades or Smart Knives to a finer pattern than we know to be ideal for the job.
Uninformed people - often those you would expect to know better - describe such blades as "heavy duty" blades.
That description might lead you to think they are stronger or more hard wearing but they are not.
When blades are made finer they become weaker, more likely to chip or break and less hard wearing.
They are a comprimise to make it possible to cut some "heavy duty" materials with the limited power that some machines have rather than the power they should have to do the job properly.