Don’t forget to order more fabric than you need, especially with upholstery. 10% is often enough. With curtains/blinds/walling you can calculate your drops more accurately.
Don’t forget some fabrics shrink when washed, others shrink when treated. Your upholsterer/curtain maker might make a mistake and replacement or additional fabrics might be from a different batch (i.e. different! not good).
Faults are a natural ‘feature’ of very many fabrics. No-one should expect you to pay for these and fabric companies will give you extra to compensate. However where the fault precisely occurs in the cut/roll is ‘random’ and although the fabric company may have given you extra the cuts you need to make might not work out. (See Fabric Tip #3)