Use 'dash off' to describe writing done in a very quick, informal manner, often without much planning.

Quick Writing

'Dash off' suggests the writing is brief and to the point, without elaborate details.

Not Detailed

The phrase can imply that the writing is done spontaneously, often in response to an unforeseen need.

'Dash off' indicates leaving a place suddenly and quickly, often right after something else finishes.

This use of 'dash off' often conveys a sense of urgency or the need to be somewhere else immediately.

The phrase is usually used in informal conversations rather than in formal or professional contexts.