Maybe what they mean is that if you have an arrangement to use a company for four hours a week, and you do not use the hours, they are lost and your need will be re-assessed. Obviously companies want regular hours, as they are a busines and employ people.
One thing to remember with direct payments is that you are the employer and are therefore liable for health and safety and NI and tax (and insurance I think) - unless you employ someone though an agency, who will do it for you.
My friend is employing a befriender for her adult son through an agency using direct payments, and it is going well. Obviously you can save up the hours to use in a block - but only if that fits in with your care worker.
Direct payments save SS money - in that they do not need to recruit and train staff, or administer their wages etc. Often the price you are allocated per hour is not as much as SS would need to pay someone themselves - so you either pay the extra yourself, or have less hours.
Karen