Generally there is no reason not to sand fill the surface. The only benefit to non-sand fill is to the installer, as he does not have the issue of transporting the heavy sand, enabling the installer to cut out a timely process to gain on margins and appear to install at a cheaper price than competitors who sand fill.

  Large areas of non-sand filled systems expand with heat during hot weather, creating sagging and ripples. Sand infill stabilizes the system without needing to install a perimeter frame to fix the grass to. Frameworks to which the grass is fixed to pose problems when the newly installed ground work settles, leaving unsightly ridges around the perimeter. Sand filled systems allow the grass surface to settle with the natural ground movement.
  Some non-sand fill systems can encounter problems with static, causing an electric shock. Clearly not something you would want to experience when children are using the area;
  Non-sand filled areas will not lay flat in contoured areas unlike sand filled surfaces due to the weight holding it in place.
  The sand does not transfer on to your clothes and is not visible as stated by some companies;
  Some longer piled surfaces without a sand fill will have very little fire resistance;
  Non-sand filled surfaces are at greater risk of theft, as cutting the product is simple. Sand infill systems help act as a deterrent as it makes it difficult to cut through the product, blunting knife blades instantly;
  As stated by some, sand fill systems does not necessarily mean less density or a lower grade of product. We will only use high grade AND high density surfaces;
  Both non-sand and sand infill surfaces will encounter similar germination of air born particles. This is simply removed by using a weed suppressor or plucking out weed growth;
  Note to dog owners – non-sand filled surfaces are susceptible to damage due to the base of the grass being clawed at by your dogs when running around.
  On certain areas where the grass can be fixed 100% i.e. around pool areas using adhesive, then a sand infill is not always needed.