sure it saves gas, but be careful coasting in neutral especially if for any reason you may need to do emergency manuevering. I coast when coming to a red light or stop sign, but I keep it in gear when going downhill on long stretches, even those with no turns. Some of the hills I go down have houses on them with driveways of course, so I keep it in gear in case someone decides to pull out in front of me and I don't have time to brake. Because you are going downhill you need a much greater distance to brake. In addition, if you do a hard emergency brake on a turn prepare to lose control. All of this is obvious now but some may not realize this when driving. Also, I'm always prepared if someone going the opposite for some reason drifts into my lane causing me to manuever. It has happened to me before.
Engine or tranny life is not so much any issue to me, especially since I don't lug my engine even when going downhill. I keep the gas steady and smoothly transition to the brake and give it a tap if I need to slow down. I choose to have an extra measure of safety for myself and others above any amount I may save in gas, tranny, or engine. For me it's about having the maximum amount of control possible at any given point in time.