"Power for altitude, pitch for speed" is a good basic rule for newbie pilots.
It tends to avoid stalls if inexperienced people are taught to not simply "pull the UP lever (the yoke)" for climbs, but add power. And generally it is the way aerodynamics work anyway - reduce or increase power without a trim change, and most fixed-wing aircraft will tend to nose down and descend, or nose up and climb, all by themselves. (High thrust-line aircraft sometimes only after a brief excursion in the other direction).
And without a power change, pitch will certainly change the speed - sometimes dangerously.
However, the dynamics of tracking a glideslope, with a heavy high-inertia aircraft, with slow-spoolup turbines, on a constant descent angle, generally work more responsively with small corrections being done with "pitch for altitude, power for speed." If you are 400 feet AGL and below glideslope, you want to GO UP RIGHT NOW - faster that turbines/thrust/power can respond. Pitch responds faster.
It is just an adjustment in habit that is part of that advanced training.