Not very, according to Evgeny Morozov:
It might … be that, contrary to some early expectations, telecommuting is not necessarily good for the environment. A 2011 article in the Annals of Regional Science found that, on average, telecommuters end up putting in more travel—on both nonwork-and work-related trips—than those who don't telecommute. (This article defines telecommuters as those who "work at home instead of going to usual workplace" once a week or more.) In other words, that they don't drive to work doesn't mean that they drive less overall. As Pengyu Zhu, the article's author, put it, "the hopes of planners and policymakers who expected the promotion of telecommuting programs to substitute for face-to-face interactions and thus reduce traditional travels remains largely unmet."
The Dish 