I've done a couple of very long roadtrips now. I've found ABRP to be an invaluable tool, but I don't really use it in realtime. It's a great planning tool when you're first planning your trip ahead of time. Get an idea of "real" drive times, planning out where you might need overnight stays along your route and which are near what chargers, etc.
It does have some advantages over the realtime in-car charging + navigation. Particularly useful is the ability to set comfort limits on your battery level, like "I don't ever want to *plan* to arrive at a supercharger with less than 12%", or "When I get to my final destination, I need to be at 65%, because I'm staying there for 3 days and there's no close fast charging" (Tesla's onboard stuff will totally let you arrive there at 10% with no way home). Also, when you're carrying significant passengers and cargo, you can put that in as additional weight and ABRP will adjust your wh/mi estimates for it (my last trip, 3 passengers, trunk loaded to the brim including the under-part, and a full frunk, I ended up estimating into ABRP an additional 1200 lbs, which is significant!).
During the trip itself, I use Tesla's in-car nav and charging selections for the most part. In the case of a multi-day drive, I generally set the in-car ultimate destination as the final stop for that day. However, I don't always do what Tesla tells me to do, either. If I know from ABRP research that Tesla has chosen an SC option that will cost me more time than ABRP's choice, I may manually set an immediate next destination to the ABRP-chosen SC and then continue my real route once I get there. Sometimes I even fire up ABRP while I'm waiting at an SC just to re-check things and re-evaluate my next steps. Sometimes that means I may want to add more or less juice to the car at this charging stop than what Tesla recommends "to continue your trip". It takes some time to develop a feel for using ABRP + Tesla in concert with each other like this, but it works out pretty well!
I also sometimes compare Google Maps routes on my phone as well, for the next short segment of the drive. Sometimes gmaps understands traffic conditions and routing decisions better than anything else. Even though it's not doing any charging planning, it can still be a useful datapoint for your evaluation.
I will say that while Tesla's in-car nav and charging usually work pretty well in the short view (~6-8h or shorter drive segments), on my most recent roadtrip I've seen it make some colossally silly mistakes as well.
The worst one I saw on my way home where Tesla's routing managed to make a horrible "optimization": On our last leg home, the car needed one final SC charging stop before reaching my house on the "normal" straight highway path home. I only needed about +10% at this final SC to make it, which is just how the math goes sometimes. But the Tesla route planner, in its infinite wisdom, decided to send me on a country roads detour to skip the SC instead! Basically because the country roads were lower speed limits, it "saved" the extra 10% of battery use and avoided that one last SC stop on the way home altogether, but at the cost of an additional 2 hours of drive time over the straight route! Needless to say, I just set my destination to the straight-path supercharger on my own. Always double-check that Tesla's nav decisions really make sense!