>>38265344Scientific research, for one thing. Insects are a crucial part of every single terrestrial ecosystem, without them they would collapse as they help to decompose many different types of matter, as well as provide food for small mammals and birds, and pollinate flowers.
Studying insects can also lead to massive breakthroughs in medicine, especially when it comes to the spread of diseases. Some of the early breakthroughs in disease treatment were actually made by joint teams of doctors and entomologists.
Entomologists also study how to prevent insects from causing harm, of course, though less so "what bug is eating your house" and more "what insects are eating all the crops we're meant to sell to humans" or "what insects are transmitting diseases to cattle".
Like, yeah, it definitely isn't the most glamourous profession, and a lot of entomologists are actually hobbyists, as there really isn't much money in it, but it's a pretty important pillar of ecological science.
Also I cannot remember which vaccine it was, but there was an early form of a vaccine (1800 I believe) which was partly made out of crushed insects which carried the disease but were immune to it's effects, and paved the way for a less gross way of the vaccine to be made after it had been verified that it worked at creating an immunity to the disease. 
