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as far as drag in an aircraft goes there is two types. Induced and parasitic.
Induced is created when the wing is at a high angle of attack as airspeed increases this drag drops.
Parasitic is created by the fusulage and all the protrusions. It increases as the airspeed increases.
Both are on a curve. There will be an airspeed where the combination of the two are at its lowest.
Combine that with an engine that operates it's BSFC at that airspeed and Pulse and glide will not be nessisary.
The other thing you could do if the engine's bsfc rpm pulls the aircraft past it's lowest drag speed is climb. The thinner air makes the engine produce less power, the thrust is reduced due to lower pressure on the prop (or stream of jet exaust). There is less parasitic drag and the wing creates less lift.
The thinner air also means the indicated airspeed is lower (the aircraft "feels" less air moving over it) while the true airspeed goes up (actual speed the plane is moving through the air)
So what airliners are doing is one big "pulse" to get to an altitude that allows the plane to cover ground very quickly while flying in low drag. The fuel burned in the climb is almost always more than what was saved during the decent. But the fuel consumption is so low at altitude that it quickly makes up for the fuel used in climb and then some.
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