It's a massive difference. I started using lightning recently, and it's crazy that you can make small transfers paying a 1 sat fee. I imagine for larger amounts the fee gets higher and at some point it's better to use on-chain, but I'm not sure what that point is (how many sats).

I use the Phoenix wallet, they say the maximum fee is 12 sats + 0.5%. Current fees onchain seem to be around 41 cents = 2112 sats. You would pay that on LN (with Phoenix, worst case) if you transfer about 420000 sats = 81.53 USD.