To be quite honest, I intend to live and work in a city (either London or a larger city up north) so I would like to be within a 20/30-minute commuting distance, be it walking or by public transport. Therefore, for me time is the key consideration but also cost too as it may be more expensive to live closer to where I work, but it could work out cheaper if I walk and don't pay for public transport.
Given walking is carbon-free and public transport is more environmentally friendly than driving, I think environmental impact is not really a consideration for me.
As for whether it should be a consideration, I am not so sure. It could be hard to calculate the impact. It could also be that you have little option but to take the job. It could also be that you do not have the money to have the luxury of considering environmental impact when choosing whether to take the job or not. I think for those who can consider it then it would be an ethical thing to do, but I would not expect anyone to turn down a job just because of the potential impact their travel might have on the environment.