You have to clear the pathway on bulkhead rows of all obstructions. In the case of an emergency evacuation, you wouldn't have to trip and fall over and impede your escape if there are things in front of you. As in the case of the bulkhead row, you can't just shove stuff under the seat in front of you.

On SQ's part however, they want you to keep your shoes on 'just in case' there is an emergency evacuation.

For my part, as much as I want to take off my shoes immediately when settling in, I only take them off only after the aircraft (any) has taken off. It is much easier to run with shoes on than socks.