THD matters, esp. in the extreme. You'll see staff electricians occasionally going on inspections in large facilities, and re-distributing specific loads onto different feeds.... a bit more on that below..... (the issue is Neutral current)
If I was
really concerned about my own location, I'm not sure I'd start by spending my money on a new generator. For a couple of reasons......
1) THD is a problem
in general, not just when you are on-generator. A basic outline here, but the most important point is the last sentence.... (Problem sources for THD are non-linear loads.......)
https://en.wikipedia.org/wiki/Harmonics_%28electrical_power%29
"Other examples of nonlinear loads are battery chargers, electronic ballasts, variable frequency drives, and switching mode power supplies."
AKA pretty much every consumer product sold in the last 25 years..... and that's w/o even going into what kind of
welder you have at home........
2) Generators can and do run out of fuel.
3) Generators can and do run low or out of oil.
Obviously, 2) and 3) are more than just a THD issue....
If I had data or systems that I were particularly concerned about, I'd want a 24x7 solution. Numerous ways to go.... one example attached from Xantrex...... quotes THD < 3%, and meets spec for ambulance applications.
View attachment DS20120912_PROsine1000-1800.pdf
As time goes on, I've become more interested in DC systems.... noise isolation is just one factor.....
Turns out, the whole of Fairbanks is on a UPS..... I've now revised what I consider a large UPS to be......
https://en.wikipedia.org/wiki/Uninterruptible_power_supply
As they are a significant non-linear load themselves, a UPS can
introduce THD locally to non-protected loads - something to keep in mind when deciding what goes onto a UPS, and what doesn't.
The other key point in the above wiki link concerns generators driving UPSes........ a low cost UPS needs to be driven by a higher wattage generator than a state-of-the-art UPS.......... something to be mindful of, esp. with small generators.
Rgds, D.