The type of car and engine is also a factor. Our Sable/Mondeo with a V6 sees some benefit from it on nearly all roads and speeds.
On the Sonic/Aveo, it only seems to help at speeds under 45mph. Higher and the little 1.4 turbo ends up sucking down more fuel with the required higher boost to pulse at those speeds. Fortunately, it shifts into the second overdrive at those speeds, so sticking near a steady engine load gets good results.
They are both automatics. I put to Sonic in neutral if I don't have a stop or other reason to slow down coming up. The Sable is a 2001. Its decelerating fuel cut off(DFCO) is no where near as aggressive as current models. Plus, there is a gate between drive and neutral on the shifter. So I leave it in gear, where the coast isn't much different than neutral in terms of engine braking.
Generally, the bigger the difference between the top and low speed of the coast, the bigger the fuel savings. With the traffic, I may only go from 45 to 40 or 35 in the Sonic. I've gotten impatient during the much longer coasts.
Honestly, I don't practice it on long, uninterrupted stretches of road. It's more I accelerate until I think the speed can let me coast to the next stop or intersection, or I time it to work with the hilly roads we got.
Yes, it's important not to cause other road users to have to make dramatic course or speed changes! Much as I like to dawdle and roll to get better economy, I always have an eye on the rear view mirror. If I see someone charging up behind me, and road conditions allow, I will accelerate so they meet me going closer to 60 mph than to 40 mph. However, I refuse to drive faster than is safe on rural roads and if another car wishes to they won't push me along any faster, I ll drive within safe stopping distances, and bearing in mind big and slow farm traffic that my be round a blind corner and as wide as the road...!