A new house needs a means of disposing of surface water, and where there is no surface water sewer or watercourse available, infiltration to ground via a soakaway is normally the solution. Whether a soakaway is feasible depends on percolation testing, and the local authority may require attenuation as well or instead.
Building regulations require adequate surface water drainage from a dwelling. In rural and many suburban locations, there is no public surface water sewer, so run-off has to be managed on the site itself. A soakaway is the usual approach where the subsoil accepts water at a reasonable rate.
Planning conditions increasingly require a sustainable drainage approach, meaning run-off is managed close to source and the rate of discharge leaving the site is limited. Your engineer should confirm the strategy with the local authority's drainage requirements before construction.