I'm probably being ridiculously pedantic here, but it's in my editorial blood!
Washing is using a thinned paint or ink to create shading as it settles in the recesses; while glazing is using a thinned paint or ink to reinforce a colour and/or help to integrate blending.
As Yakface says, both alter the hue of the colour underneath; so while they are very similar, there are differences between the two. They do get conflated – and GW (and a lot of the miniature painting fraternity/sorority)seem to use them interchangably.
As to why some techniques are thought of as 'better' than others, it's generally down to a sense of 'fair play'. For example, when creating shading, dipping creates results that are comparable to traditional painting methods (like blending)– and is far easier.
At the top level of painting, other techniques blow the effects that are possible with dipping out of the water.
In regards to your question, which techniques do you want to know about? There's almost as many techniques as there are painters!