Usually the answer is that they can't be without it at all.
So I never recommend Apple laptops for business owners unless they have a spare... a spare "anything" will possibly suffice especially if everything they do is online.
I only tend to buy Dell business laptops: great build quality and a 3-year next business day onsite warranty are worth every penny imo: Not as flashy and fancy as the XPS stuff but they have/had quality issues (as the commenter below mentioned).