You can save on labor in the short term. You'll pay for it another way long term, either by losing overly stressed staff or by having someone too critical call in sick at a bad time.

Or anything else. Perhaps they're involved in a car accident and cannot get into work even if they're not injured, perhaps someone critical dies unexpectedly, or they get head-hunted by another company and leave without giving you warning since they obviously don't need the reference.

So many bad things can happen when you only have a single point of failure. Companies will pay for multiple internet lines but refuse to hire additional staff. One of those things is not like the other.