Man has been cooking meats with fire for almost a Million years...."Modern Day" BBQ (whole Hogs etc) is usually traced back to Colonial times...400 plus years ago...generally in/to the Carolina Colonies.. To my knowledge the use of tin foil in BBQ (As A Crutch) is a modern "fast food" practice..only being in place for maybe 3 or 4 decades. ~~ Only in very recent history does man need, a Roll of Tin Foil, A Pound of Brown Sugar, A Quart of Apple Juice, Swaddling Clothes, and a 48 Quart Igloo Cooler to Cook ..XYZ....(You fill in the blank)
When to foil? Don't!! ... Learn to Cook instead.
Why Foil?... Other than the obvious..I don't have a clue.
Course by that logic we should all abandon our cars and just walk everywhere.... heh-heh.
Foil really is just personal taste, no real right or wrong as long as you get the results YOU like.... unless you are doing competition smoking then its the resulst the judges like.