If by "using my eye to focus" you mean looking through the view finder, then a distinct advantage of something like DSLRFocus is when you deal with faint objects that are hard to view through the view finder, and moving back and forth between a bright star and it is impractical.
I find I only rarely get a perfect focus by looking through the viewfinder, I need DSLR to get the last little bit.
Roger.
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