Bottom line - I don't see what difference it makes if the home switches are off 1,10 or 100 thou. You shouldn't ever be working near the limits or using them for anything. I rarely eve loo at them.
(there are reasons to take them into consideration like whether you have enough room to set a fixture offsets or whether soft limits are going to be exceeded but for the most part I never even look at the machine co-ordinates.).
Maybe I'm missing something.
Sage
Machine coords and accurate homing are very important. One instance is you set up a job that you need to run a lot of, you have a fixture of some sort so that you can place the parts in for accurate placement. Ok so you have 100 done and its getting late but tomorrow you will finish the rest so you shut down Mach and go home. In the morning you come in, reference your machine and away you go, if you didnt have accurate home switches you would need to find the zero position of your fixture again.
Another instance may be you are doing a one off, its a long job and you need to go home, its either leave it running, leave Mach on all night or if switches are accurate you can shut down and next day home and go straight to where you left off with confidence.
Another instance would be on a lathe, you set the tools up for zero to be spindle centre on the X axis, if you have no way of homing accurately you need to take a cut each time and set the dia for your master tool by measuring the stock dia. I have accurate homing so I know once I have homed I can tell Mach to cut at 30mm dia and it will be 30mm dia and I then have no need to set the tool coord every time I start Mach.
Hood