As I understood it, powerchains are used particularly to close gaps for people that have had extractions.
My ortho hasn't mentioned using them for me (I haven't had extractions and currenly have no gaps) but you never know. I will ask him about them next appointment.
Some mild flaring can be corrected with a Hawley retainer provided you have spacing and your bite is not very deep. There are many reasons a doc may choose not use chains but they are most commonly used for consolidation of minor-moderate spacing.