Of course there are huge savings, but there’s a typical death spiral when a magazine goes online only:

a) optimism over the new format, fresh start etc.
b) realisation that print might be 50 percent or more of total costs, but advertising revenues tend to fall by a greater amount and there’s no way to make up for lost cover sales revenue.
c) the staff cuts begin – usually starting with editorial and quickly leading to even fewer readers and hence less advertising revenue.

There are answers to the problem but not within most existing publishing business models.