Most companies don't allow you to do work on non-corporate computers, for intellectual property/security reasons. They might not figure out anything is amiss if you merely add some parts to the computer they provide you, but that's about it. Our corporate network is locked down and you can't add random computers to it -- if something unexpected does get plugged in, someone in IT will be by eventually to see what the hell it is (and in the mean time, that computer is only getting guest network access).
Let me clarify my statement: Most *employees work at companies that don't allow you to ...
Yes, I'm sure most startups are lax, but big corporations are not, and there's way more engineers in total working at big corps than at startups. When I said "companies" I didn't have startups in mind.
It definitely depends on industry. In the healthcare and finance space, that's been the case. But in other parts of the industry, including at most tech startups, BYOD has been acceptable. Many places use NAC + policy scans to validate your personal equipment meets their policy bar (and you may need to run a specific piece of agent software to be allowed on the network), but other than that they seem to not care much.
