Scientific knowledge grows organically, like a tree.
Every piece of published research is like a new bud on a twig. The bud is connected to every other bud on the tree. Two buds may be very close together, on the same twig, or very far apart, so that to trace the connection one would have to follow twigs and branches all the way back to the trunk and out again along other branches and twigs. Ultimately, all scientific knowledge is one. It is the connectedness of science that give us confidence in its reliability.
The amount of research being published today is so great that no one can claim to know the overall shape of the tree. The last time I checked, there were upwards of 100,000 scientific journals. It is virtually impossible for any one scientist to become familiar with more than a single branch of the tree.
A rule of science requires that every published paper cite all previously published work that bears upon the same subject. The citation rule assures that new research is firmly connected to the tree of science.
As it turns out, only about half of published papers are cited by subsequent research. That is to say, about half of the twigs on the tree of science are dead ends. They could be snipped away and the tree would grow as robustly as ever. At first glance, this might seem promising. Good horticultural practice suggests that a tree grows best with judicious pruning. The nutrients for growth, in the form of funding, are limited. Snip a branch here and there, and the other branches will grow more vigorously.
The problem is knowing which branches to prune. Who can tell which scientific research being done today will be the start of a fruitful new branch of the tree and which is destined to be deadwood? Significant work may go unrecognized for years following its publication. Without some possibly wasteful measure of support, promising ideas may fade before they have a chance to establish themselves in a citation index.
More worrisome, science might become a self-perpetuating aristocracy, rather than an open meritocracy. It may be necessary to tolerate a substantial amount of fruitless research in order to insure that science remains open to the gifted young, and to others working outside of elite research establishments.
It may be that science grows best wastefully and wild, without the horticulturist's tidying hand.