[henry quirk]

The prime difference: writing TENDS to eliminate ambiguity as well as preserve the codification of thoughts across time and circumstance while speech is OFTEN muddled, meandering, and utterly dependent on the flawed memory of the listener once the speaker is done.

Any psychological impact either route has (on writer/reader; speaker/listener) extends out from this difference.

That is: one is FAR LESS LIKELY to 'interpret' the content of writing (IF DONE RIGHT, the meaning of the writer is plain and can be revisited indefinitely) than the content of speech (there's a lot of truth to the notion of 'only hearing what you wanna hear').

Liberal interpretations USUALLY lead to mistakes while more narrow interpretations, of course, REDUCE the chance of error (in responding to the writing).

Another way to look at it: speech TENDS toward 'noise' and writing TENDS toward 'signal'.