To Hindus, the cow is a sacred animal, so they do not eat beef or touch any part of a slaughtered cow. This is an important consideration with regard to the tannery in the novel because it explains why so many Muslims initially worked at the tannery and, in part, why Rukmani was disappointed that her sons went to work there.
The answer to your question can be found in Chapter Four of this moving novel. Now that the tannery factory has been completed, this tiny and isolated village experiences a massive change that it has hitherto not known. As always, the changes are both positive and negative. The villagers, for example, are able to sell their produce at a higher price to the workers, but prices have been driven up for them as well, so they are unable to afford the products that they were accustomed to buying. In addition, the tiny village that has served as our narrator's home is turning into a town, with all the noise, commotion and bad smells associated with this new state of affairs. Whilst Kunthi likes this, our narrator bemoans the changes:
Already our children hold their noses when they go by, and all is shouting and disturbance and crowds, wherever you go. Even the birds have forgotten to sin, or else their calls are lost to us.
This novel therefore presents us with the many faces of "development" and how change in this example has both positive and negative consequences for this tiny isolated Indian village.