If your home qualifies as your principle place of business, then you do have a main place of business, even if you can't use the home office deduction due to the exclusive use rule.
For example, you might use your home for bookkeeping, calling clients, and storing supplies. That may make your home your principle place of business. You could only take the home office deduction if you used part of your home for business only (like a spare bedroom or section of the basement) and did not use the same area of the house for family or personal living space. But even if you don't have an exclusive area in your home for business, you can still call your home your main place of business even if it doesn't qualify for the home office deduction. And in that case you can deduct your transportation expenses (subject the usual rules about keeping records, etc.)
