Creating a successful business doesn't come cheap and you can't afford to waste money, so why would you be expected to subsidise your online customers?
Any online venture needs to pay for itself, and every penny that you spend should be returned to you, with interest.
You may want to promote your business, your products or your services; you may want to increase leads and encourage repeat business; and you may want to reduce costs.
But let's be fair about it - these are probably the same aspirations that you'd have even if the Internet didn't exist.
By properly planning your online strategy you will gain a valuable insight into how feasible your venture is, what success criteria to measure and when to expect payback.