>>1091All the time? No.
You only use it if you
feel it's necessary. Either because of context (as you mentioned, when talking with co-workers, boss, etc), or simply because you feel more comfortable using formal speech. For example, when asking for permissions to translate something, or when I'm discussing with jap anons here or in other places, I tend to write in formal form even when it's not really necessary; I'm just showing them that I was willing to learn their language to have a better communication, and that while I was at it, I was going to use it correctly. This hasn't stopped me from going full dick on futaba or other forums, à-la Makise Kurisu, if the heat of the moment made me do so. Practically the same when I go full autistic in english, to be honest.
So, tl;dr this is highly personal, use whatever you feel comfortable with. Most jap anons write informally and with slang, but it's not odd to see the one using -masu and desu everywhere.