As for BBK, I think it may be an order from above.. Barclays in the UK is shedding off 1000 employees, so it might be a trickle down effect. This happens especially in multinationals, where the decision to lay off people is made in HQ, and all branches are supposed to implement.
Restructuring can come from two aspects: change of leadership, and cost reduction. For example, change of CEO - the new CEO may have a different structure in mind to improve effeciency. Also, in response to declining sales, management may decide to reduce costs, hence a restructuring.
My experience, whenever someone mentions restructuring, people go home. Not always..but in MOST times, retrenchment will happen.