Alice buys a car from a car dealer Bob.
She has yet to join LN so she opens a channel with Bob contributing a significant sum (price of the car), Bob doesn't contribute any funds to the channel. Entire channel balance immediately transferred to Bob with the first commitment transaction.
This would probably not be a good idea for either party. Both parties would need to pay higher fees than if they had covered the tx fee for an on-chain transaction. There is also no guarantee that either party will facilitate LN transfers in the futures and be willing to pay/accept what the other party deems to be a reasonable LN fee.
It would also not be unreasonable to expect you to receive a LN payment via this channel, and subsequently spend the majority of said payment in a subsequent LN transaction. If this were to happen, then you could attempt to broadcast a settlement transaction that is not the most recent, that would result in you receiving more BTC than what you and the dealership have most recently agreed to -- in this situation, the dealership should normally be able recover then entire balance within the channel before you can spend the portion spent to you, however doing so would incur an additional tx fee that the dealership would need to bear in it's entirety in order to claim an amount that they are due anyway....and you are not risking very much/anything when you attempt to steal these funds (at most a nominal amount).
Alice plans to use this channel later to receive salary from her employer.
If you do this, then the dealership might see that your portion of the LN channel is receiving the exact same amount on a very regular basis, they might be able to reasonably conclude the amount of your bi-weekly (or whatever frequency) paycheck, harming your privacy (the exact information they will know is that the balance of your channel is increasing every other Friday by the same amount, they will not have proof if you are receiving this payment, or if you are acting as an intermediary. They will also know the channel that is sending the payment to you, they wont know if that channel is sending the payment directly or if they are acting as an intermediary).
Also, if you only have one LN channel open, then you will need to accept whatever LN fee the dealership is charging (they can change the LN fee at anytime without notice), or else close/settle the LN channel, delaying your access to your money AND be forced to pay a very high tx fee.