If you're converting some symbol with a method that assumes the string, than you have additional to_s -> method -> to_sym convertation
time ruby -e '100_000_000.times { "A".downcase }' # 6.70s user 0.06s system 93% cpu 7.254 total
time ruby -e '100_000_000.times { :A.downcase }' # 8.39s user 0.04s system 99% cpu 8.497 total