If you file a Schedule C with your family's Form 1040, all business expenses will be deductible.
If you don't file a Schedule C but claim your needlework income on the front side of Form 1040, your business expenses will not be deductible.
Why would you want your business expenses to be deductible? Because when they are, you are able to reduce your business income. In turn, this reduces the amount on which your family owes taxes and increases the amount of money you actually have to spend.
Business deductions include books, journals/magazines, office supplies, postage, kit expenses (materials, printing/photocopying of chart and directions, plastic bags, freight, etc.), festival expenses (transportation, hotel, meals, rental car expense, tips, etc.), insurance, mileage when your car is used for business purposes, entertainment expenses, and so on.
You also can -depreciate- your equipment used in your business, such as a computer, software, kitting table, drawing table, filing cabinets, desks, and so on. Depreciation is a kind of deduction you claim over a period of several years rather than all at once. ("All at once" is called a write-off.)
Another important deduction is for an office in the home, which is quite common for designers. If you claim a deduction for office in the home, this can be a large sum, as it includes part of the mortgage or rent, heating, electricity, property taxes, and so on.
Obviously, a Schedule C is worth the effort.
If you claim the deduction for office in the home, you will reduce the amount of money you may put in your retirement fund. This is because that maximum is based on the number shown -after- subtraction for the home office deduction. (Taking the office in the home deduction also affects the amount of profit on which you do not have to pay taxes when you sell your home at retirement and move into something smaller and less expensive.)
Unless you are going hungry, I propose that the retirement money later is more important than the deduction now. This is your decision, of course. Consult your accountant if you need help in constructing scenarios.