If you're talking from H-Brace to H-Brace, I agree _ run on TIGHT string.
BUT, If you're talking about a LONG fence, I've done the one wire trick and still had the wave effect going on due to wind, complacency, etc.
What we do...
Wife sits down on 4-wheeler with UNLOADED (I check it myself in case she's mad at me) deer rifle and she looks thru scope at stopping point.
On my 4-wheeler, I drive down to where I want the H-Brace, hold a T-Post steady, and she guides me back and forth till it's right.
At times, I use the portable auger and sit the steel post then/there OR drive the t-post in and come back later to sit the steel.