I tension by hand and ear for most conventional wheels and I also use a tension gauge to double check my work or when I am building unconventional wheels (radials).
If I don't have a tension gauge at hand when I am building a conventional wheel I don't fret it... the last wheel I built was for my friend's touring bike and I finished the build the night before he left while sucking back a few cold one's on my patio.
6000 km of loaded touring later and the wheel is still true to within 5/1000 and it was built using the bike's fork as my truing stand.
I have a set of mtb wheels that are rolling around under my 240 pound friend and these wheels have never needed to see a spoke wrench... I used the tension gauge and had these dialled in to a tolerance of < 2/1000 and they have not changed.
Getting even / high tension is much more important that getting maximum tension in a wheel and I usually build just below the advised maximum (90% to allow for any adjustments)... if the spokes are so tight that you are rounding off the nipples or destroying the rim you are doing it wrong.
I encourage my customers to bring their wheels back for a free inspection as I like to inspect my work but very few do as they tell me their wheels remain as perfect as they were when they were first built.