REDEFINES - why would I want two names for the same memory?

Saw REDEFINES in a record layout. Same bytes described two different ways. When is that useful and when is it a footgun?

Useful when the same file record is type A or type B depending on a code in the header. One layout redefines the other.

Footgun when people redefine numerics as character and then do math, or forget which view is "current."

Also common for breaking a date PIC 9(8) into YYYY MM DD fields without MOVEing.