Google hasn't been in some places in NJ (the most densely populated state in the US).

It's still a useful tool (even if it's not complete).

I tour outback Australia. No internet nor mobile/cell service in most outback/rural places. Paper strip-maps work for me. This will also happen this June-July when touring Cape York. There (Cape York) you are lucky to find a telephone of any sort...

Which exit?

True. Yet one benefit of electronic navigation is to indicate exactly where you are, which means distance and time to destination. This works very well offline.

See for example bRouter suggested route between Brisbane and Cape York. Could have been generated offline.

You can download maps to your smartphone. It doesn't make much sense to rely on having cell service anywhere. Especially, since it's easy to download maps.

It's "what exit?"

While the Electronic Navigation may be great to tell you exactly where you are, the time to destination means nothing. Road and creek conditions will throw a wrench into that idea.

Try riding those roads and you will see what I mean. Then of course there is the issue of keeping your unit charged up - best to turn it on only when you need to know "exactly where you are".

Depending on the software you use, or with mental computation, ETA will consider your average speed, given the terrain, into making its forecast. So, wind, mud, fatigue, etc. can be factored. IIRC, my Garmin Edge had optimistic estimates. Locus is somewhat better. With some experience, I'd say that it is reasonably accurate (10%?)