It's also applied to switching dialect, word choice, and even accent. Lots of people in the US who grow up with any kind of regional or ethnic accent or English-variant end up being capable of code-switching to Standard American English, especially if they move around much and/or attend school somewhere outside the area where their dialect is normal, though even regional schools will provide some social pressure to avoid non-standard accents or dialects that are common in their areas. AAVE (African-American Vernacular English) is a commonly-cited variant from which one may wish (or feel strong pressure) to code-switch to SAE, but similar (if less race-fraught, so perhaps not directly comparable) pressure exists for people with strong Bostonian or Appalachian or rural-midwestern accents, or most anything other than SAE.

The positive reason for this, is that it allows potentially extreme variants and dialects to co-exist while letting everyone still communicate clearly with others (by code-switching to whatever's considered standard). The down-side is that it often exists alongside negative stereotypes about those who can't, or choose not to, code-switch to SAE (but, of course, refusing to becomes its own counter-signal for very high status—Fussell, for instance, observes that adhering to SAE is a middle-class and up tendency, but not among "old money" or his "top-out-of-sight" rich, since they don't need, at any point in their life, to give a damn whether some employer or other gate-keeper judges them worthy or intelligent or whatever).

I didn't get what code switching meant until my first job out of college. I had a coworker who would copyedit what I wrote to a level that would impress an English professor. It was great, he made me sound so much smarter to the rest of the company. When we became Facebook friends, I was surprised to see that he had a totally different manner of speaking to his friends.

I can't speak for the GP commenter, but from my own experience being non-binary, I have to expend cognitive energy every morning thinking about what I'll be doing that day (what meetings, any errands, etc), before deciding what clothes I can wear. If I'm staying home all day, with no meetings, or only meeting with trusted colleagues, I will dress differently than a day where I need to go to a store, or if I need to meet with coworkers I've never met before.

For trans people, just existing without conflict or judgement from others is a constant struggle between society's normative expectations and the desire to express who you really are.

Yeah that’s basically it. Working from home I can be in a t-shirt with no bra and a days worth of stubble and nobody is the wiser. It helps that I pass without makeup though.