If you work from the office, and they have tight security, they might frown upon bringing personal devices to connect to the internal network.
Also, some people might not have dev environments set up on their personal devices. Heck, a lot of people only use the internet through their smartphone, when they're not at work.
My employer allows personal computing equipment at work, but has a separate, completely isolated network they connect to. You're never allowed to connect them to the company network.
Also, some people might not have dev environments set up on their personal devices. Heck, a lot of people only use the internet through their smartphone, when they're not at work.