Home office and mileage deduction/transportation expeses

[Uwe K.]

I was reading about and researching this over and over again, books, IRS pubs, here, elsewhere. I cannot get a conclusive answer even in forums with seasoned CPAs debating this topic.

That much is clear:
- If you have a qualifying home office, you can deduct the related expenses
- If you run errands for maintaining etc. you rental property, you can deduct the mileage.
- You cannot deduct commutes, e.g with No home office, the way from and to your home would be the commute, anything in between is deductible (in simple terms)
- If you have a qualifying home office, you may or may not have the principal place of business in your home (e.g. home office, but you rent another office space)

Here is where I am not clear:
Can I have the principal place of business in my home although I do not have a qualifying home office (or alternatively may have one, but do not claim it)? I have no other office space, just a PO box that's too small to fit a desk. Do they accept that? That's what even CPAs debate.

The answer to this question then influences my main concern: mileage deduction.
If I have to drive to a rental for some maintenance (no other stops to keep it simple), can I deduct the mileage, if I have an office in my home, but not an "IRS type qualifying home office", that I actually use for business purposes?
Or back to the previous question: can i have the principal place of business in my home without having a "home office", but having an office in my home. (I am wording it this way because IRS pubs word it this way, on no monkey knows what they actually mean).

I also remember a few years back I may have read something about that if you expect to go to a place for a year or more regularly, it will be considered your workplace, so the drive will be a commute, no matter what. Well, in many cases, that pretty much fits any rental if you manage it yourself.
But I can't find this anymore.

What do you do? Has your "system" survived an audit?

All this assumes you work out of your home, are not an employee, and all the other little requirements they have.