I love OnX. Between it, and the USFS PDF maps (which can be keyed to GPS using other free apps), I've been able to do a bunch of exploring.

For example, last December, I drew a tag for the Whetstone mountains in AZ. The primary route that everyone used into the western side of the mountain range was a 2.5 hour drive in from the far west, with significantly challenging terrain toe cross. However, between OnX and the USFS maps, I was able to find a route from the south that had an unmarked, but official, USFS service road through private property.

Without that kind of info, I would never have even thought to approach the gate into the property (other hints at arrival help - there was a USFS placard saying to keep gate closed). It saved me dozens of hours of travel during the trip as we were staying in a nearby town.