Where I live dew point gives a very strong indicator of our overnight low temperatures, especially in winter. Looking at dew point can tell me whether to expect frost or not and if black ice is likely to be an issue in the morning.
But yeah, treating those guidelines as anything other than a loose suggestion is meaningless.
https://www.weather.gov/arx/why_dewpoint_vs_humidity
> less than or equal to 55: dry and comfortable
> between 55 and 65: becoming "sticky" with muggy evenings
> greater than or equal to 65: lots of moisture in the air, becoming oppressive