First off, I would like to thank Ray and Paul for taking and answering my question about sector lines and GC III in today's chat. 
That you allow us to pester you with questions and give you our feedback is most appreciated.
I was disappointed to hear, however, that sector lines won't be able to be turned on in the game when it is released, and I wanted to explain a bit more why I think they are important by using GC II as an example.
On very very large maps, it becomes very difficult to scan a large stellar empire without some sort of major guideline on the map. The problem I have is, as I drag the mouse along, the map itself might move up slightly or down slightly which can add up after a while, and cause systems to be lost that I am looking for. And if I am trying to look for various features or perform some sort of survey in my head that the game doesn't provide (# of ships of that do X within an area), if I lose track of where I have already looked, it can prove debilitating.
This is where the sector lines ala GC II came in. It would let me know that I hadn't missed something and/or I hadn't "strayed off the path" as I was moving across my empire.
A couple of screenshots below might help show what I am trying to say:
The one above is pretty much the furthest one could zoom out of the map on GC II. It shows all of the individual tiles, but in slightly more pronounced lines, it also shows the sectors. This allows me to move the mouse along those sectors as I look for various things, and goes a long way in making sure I don't get lost or miss things. Or worse, double count something I had already looked for.
That screen shot above shows a close look at the same map. What I would do is move left/right or up/down using those highlighted lines to keep me "on the path" as it were.
With map sizes being up to four times as large as they were in GC II, I think something like this is going to be even more important in GC III than it was in GC II.
Now I understand that the shift to hexes might make sector lines/major gird lines difficult to implement and look nice. But it is something that I really feel is critical as map sizes get larger and larger. Even if only as a toggled setting via the option screen or something advanced users could set in the preference file.