The phrasal adjective cut and dried describes things that are (1) prepared and arranged in advance, or (2) ordinary or routine. The phrase’s exact origins are mysterious, but it seems to date from the early 1700s—when it was used in roughly the same manner as today—and it presumably comes from agriculture.
Cut and dried is often written cut and dry, which isn’t a serious error because dry works as an adjective with essentially the same meaning as dried.
The phrase can take hyphens when it precedes what it modifies—for example:
It appears to be a cut-and-dried tale; noble activists and caring government come together to do something positive. [The Daily Star]
When I tell people that I study engineering, they often assume it is a cut-and-dried trajectory. [WSJ]
This hyphenation is normal for phrasal adjectives that precede what they modify, but we can also think of cut and dried as a pair of coordinate adjectives separately modifying their noun, in which case there is no need for the hyphens.
When the phrase is a predicate adjective, as below, there is no reason to hyphenate it:
“I thought it was pretty cut and dried,” said Ms. Long, who is a registered nurse. [NYT]