Opening and ending songs are common additions to a show in most forms of media, game, films, tv shows and, of course, anime. They're iconic songs or jingles that serve a variety of purposes, be it to act as a catchy jingle that hangs in someone's head to bring their mind back to the show or to reflect what the show is about as a whole.
However, these songs are arguably far more important in the realm of animation, western or eastern regardless. Very often creative use of clips and music are used to give a far greater impression of the show and even provide hints as to what happens in the show or have an emotional impact all on it's own. Personally an opening or ending song can be the greatest take away from an anime.
"But how is this different from films and western tv shows? Don't they do this too?" You may be asking.
This can be the case for some live action shows or films but the main difference is this, Western shows use this time more to credit the actors and actresses who act within the show and then within the credits normally a song is played at the end of the show... and that's it. Animated openings and endings talk to the audience a lot more for those with a perceptive eye.
"So why are you writing out all of this like a mini essay?"
I really just wanted to feel somewhat academic whilst creating a Favourite opening and ending thread by pondering the significance of these segments.
As meh as I found most of the show, one opening that has stuck with me as one of my favourites is the first opening of SAO.
Here's an english version