Differences Between Formal and Informal Communication
This particular dimension of communication is not so much a style as a choice that is usually dictated by the context and situation.
It is also associated with cultural differences, with Asian cultures seeming to be more formal in tone, given similar situations, although it's not a good thing to stereotype.
Also, particularly in Western society, more and more communication is done "informally", both in structure and stone. No doubt digital technology is part of the reason.
A mismatch (one person speaking formally, another informally) is likely to evoke misperceptions if parties are not aware there is that gap.
The formal speaker may see the informal speaker in the conversation as lacking respect or manners, or even as being illiterate and ignorant.
On the other hand the informal speaker may see the formal speaker as being a "stick in the mud", putting on airs, or otherwise trying to impress.
Neither need be true.
Informal Style
Communication is governed by strict rules regarding such things as: forms of address, ways to address persons of different ages and statuses, topics which can and cannot be discussed, etc. Communication in many respects is highly
ritualized.
Informal Style
Communication is less bound to specific conventions. Persons have more flexibility in what they say, to whom they say it, and under what circumstances. Informal communication might also be demonstrated by the use of the first name, for example.