1070 has 8GB of VRAM, so it should be fine to leave it on.
The auto-configuration will give you:
512x512 shadow map resolution at 4G, shadow caching off
1024x1024 shadow map resolution at 6G, spot and sun shadow caching on
1536x1536 shadow map resolution at 8G, spot and sun shadow caching on
You can of course tweak these post facto.
Shadow caching trades draw call throughput for video memory--with it enabled you have fewer draw calls due to reusing cached shadow maps (rather than reissuing draws to re-render them), which reduces throughput on the driver thread, which is actually the long pole on the CPU almost 100% of the time, and often the long pole in total unless running at very high resolutions/GPU workloads.
Someone else asked about reducing video memory usage to increase texture resolution. One possibility is dropping from SMAA 2X--the temporal history buffers can be non-trivial (luminance, depth, velocity) if you have an aggressive final scene resolution.