I know what you mean. part comes down to what Shibui mentioned and part is down to aesthetics and tastes.
some folk dont mind heavy, thick branches or sub trunks, and just cut them back hard, if there are nodes to taper back to, while others prefer to cut off all the sub trunks and grow new aesthetically pleasing branches, what happens with the latter is you end up with a massive trunk with branches that dont quite match for many, many years.
in naturalistic bonsai, most of the heavy subtrunks are kept, if thats what you like have at it mate.
in the tree you posted, you can see where the 4 heavy branches removed were all in the same area and looked to be causing a swelling, in that case maybe that reduction was best. every tree is different right. there are better examples.