It's pretty much the same as in the other thread, anything that can be done landside can also be done at a transfer desk or the boarding gate. The only difference is there is less time available when boarding is about to begin!

I don't know why you think that you might be obliged to go landside. The computers are the same and the staff may even be the same for SQ - they may go airside after they close up the check-in counters (but not for KL obviously).

For example, if for whatever reason they had to send a message to Singapore ICA to get approval for you to board the plane, there is plenty of time if you are at landside check-in 2 hours before, but there might not be enough time for a response if the gate is going to close in 10 minutes.