Two different mindsets:
Jigsaw is a means of building up detail over time...refining a solution after an initial understanding of only the most critical ideas/elements/concepts.
Sequential is when at any given time the full details (applicable to that instance) must be known and understood. Details cannot be refined over time, they must be actef upon at a specified point in time to the full extent.
Jigsaw is the means by which design information should be reviewed...build up a more detailed, interdependent information overtime (by what ever means).
Sequential is the means by which things should be constructed. All information known at time og implementation (the term 'facts known' means to represent that risk has been managed via acceptable means).