Knowing that my new tank was going to be SPS dominated, I used very little rock for the space I have (72 x 26 x 24). I have a total of 90+ pounds of live rock in a 195 gallon tank. I created two small islands with just as much space behind the rockwork as there is in front. My goal is to have limited SPS frags grow into large, mature colonies that fill in the space. I only have 80 pounds of sand in the tank as well. I find it's extremely easy to reach every part of the tank, and the added water volume is welcomed over cluttered rock work. Over time, no matter how good your flow there will inherently be dead spots as corals grow. Since detritus is an enemy in an SPS tank, limiting the rockwork to have access is key longterm, IMO. The old adage that you need 1 -2 pounds of liverock I feel is inaccurate.
As long as you stock responsibly with fish, I feel there's no need to have that much rock...and many of the more modern, minimalist tanks prove that point. Being able to effectively remove detritus from wherever it may settle is a great way to avoid anything ever building up.