Many retail photographers don't make any money at all, and instead subsidize client shoots out of their own pocket.
Sadly, most don't even realize they are subsidizing their clients, because they don't know how to track expenses against income which is basic accounting.
There is a difference between an "accounting subsidy" and an actual cash subsidy. It would not be at all uncommon at a certain level for a photographer (or other part-time businessperson) to not consider the pro-rata cost of car ownership, just as a for-instance. It would also not be at all uncommon for the part-time business to be then "operating at a loss" in an accounting sense, when all such costs are included.
However, things like car ownership (and, let's face it, often the photography gear itself) is in reality sunk cost. Just because standard accounting rules and the IRS allow you to consider those expenses as part of the business doesn't mean that you must consider them so.
Many businesses wind up adding a net dollar gain to the total family income.
Some of those businesses would be, if the accounting were done "correctly" operating at a loss. Some of them probably DO the accounting correctly and reap a neat little tax benefit for a while, while still adding a net gain to the family income, which is pretty slick.
Some businesses are in fact operating at a net cash loss, and that's too bad.