Yes, this is true. It's profit that matters. There is a set amount that you can claim for home working if you're registered as self-employed and don't want to have to work it out as a proportion of everything. I just found a link to the flat rate for simplified expenses: https://www.gov.uk/simpler-income-tax-simplified-expenses/working-from-home

Not sure about depreciation - that depends on how you complete a tax return, I think. I don't claim for depreciation. I just buy a new computer when I need one, and put it down as a business expense. When it's dead I'll buy another one as a business expense. I think if you want to claim for depreciation, you have to count it as a capital thingy, which allows for depreciation and is slightly different. Or something like that! 😬