How does conservation benefit the environment?
In a broad sense, it helps keep life on Earth robust and able to handle extinction events.
Species conservation preserves organisms, but in so doing, it helps keep the Earth's genetic diversity high. High genetic diversity is essential for long-term life on Earth as periodically extinction events happen (volcanic eruptions, glaciations, asteroids) that kill off large numbers of species. Having a large "reservoir" of genetic material increases the odds that some form of life will survive after one of these extinction events.