This now-more-prevalent practice has not been welcomed by everyone. Critic Andrew Clark of The Financial Times wrote this mostly-critical piece, wherein remarks from the podium are called representative of "insidious" thinking about concert music on the part of presenters who "fear that classical music may not be sufficiently communicative or 'entertaining'. Mr. Clark goes on to say that "[y]ou don’t have to explain jazz to anybody" (!) and that concert music needs no explanation. Thanks to A. C. Douglas for pointing out this piece and pulling some of the more negative quotes from it.
Mr. Clark says that discussion of the music from the stage:
. . . limits the imaginative scope of the music. Listening to someone discussing a piece of music before you have a chance to hear it pre-programmes your responses. The music has no chance to communicate freely. You are left with a number of objective ideas about what to think and feel, circumscribing the subjective impressions that music seeks to create in the listener through the medium of sound.
This is not inherently true, anymore than reading program notes or having prior knowledge of the piece restrict the listening experience. Every experience one has with a given composition, composer, style, or body of music (maybe even bad experiences) adds to the totality of one's musical knowledge.
Mr. Clark closes:
Of course, it doesn’t do to be too purist. I recall several occasions at the Cheltenham festival in the past 10 years when festival director Michael Berkeley introduced a concert from the podium. He happens to be a composer but, unlike most composers, he is also a relaxed public speaker. He thinks as a composer does, but knows what information will be most relevant in advance. Exceptionally the formula worked. But please note - it was the exception.