What the sand is for
Jointing sand fills the gaps between the blocks and helps keep the surface stable. It is doing more than simply making the drive look finished.
Why cleaning removes it
Moss, weeds, dirt and loose sand often come out of the joints together. How much is lost depends on how full and compacted the joints were before cleaning.
Wait until the drive is dry
The joints are easier to judge once the paving has dried. If they look low or empty, fresh kiln-dried sand can be brushed in during suitable dry weather.
Check what is included
Cleaning, resanding, stain treatment and sealing are separate jobs. Make sure the quote says which of them are included.
Not sure about your own property?
If you are in Ryedale or nearby, send Will a couple of photos and a short description. He can usually tell you whether the surface needs a closer look before quoting.