Sorry Uhoh, I got your point, but the Giuco Piano is a bit more "boring" than almost anything I can think of after 1.d4. The Petroff is not the most exciting opening either.

I'd say that there are many tactical possibilities even in d4-openings. If you are looking to get the positions that look like somebody just dropped the pieces randomly onto the board, you should have a repertoire. And if you want to avoid them, you might benefit from a repertoire. I know that most people say that e4-openings are more tactical, but even the "boring" English offer plenty of chances. Look at Marin's recent work e.g.

I'm kinda surprised by the lack of responses here, and the one response I did get didn't really address any of the serious questions. 

Do you really think everyone who plays chess should have an opening repertoire? Even my nephews who played in their first tournament a few weeks ago and have 200 and 300 USCF ratings? I'm happy that they start with center pawns and usually (not always) remember what I told them about bringing out pieces instead of just making a bunch of pawn moves in the opening. I think it's a little early to introduce them to the Giuoco Piano or Colle System.

What about strong young players who are working towards becoming masters and grandmasters? Shouldn't they experiment with a variety of openings to learn to deal with different positions, rather than narrowly playing the same stuff all the time? I knew one kid who hit 1900 at 12 years old, and he never played the same opening against me twice, just to keep me guessing. In skittles games, he'd even play really oddball stuff like 1. f3 just to see what would happen, though he wouldn't do that in serious tournaments.

It just seems to me like opening repertoires are for relatively serious (non-beginner) players who don't have time to study everything, so they pick a few openings/types of positions, and they stick to them. But those who aren't that serious about the game yet, or those who truly want to learn everything so they can become masters/grandmasters some day, might not want to limit themselves that way.

Which brings us from "who" back to the questions of when and why, not to mention what exactly is a repertoire? 

Is it just one opening for any situation, or a limited number of responses? For instance, I used to just pick one response to 1. e4 and always play that, until I decided to switch to a different response. I ended up going back and forth between e6 and e5 as my main response to e4 every 6-12 months. Lately, I've decided to play both regularly, depending on my mood and opponent, instead of having a single repertoire choice. It's still a repertoire, but not as narrow as before.

Some questions about opening repertoires: Who, what, where, when, why, and how?

No, I'm not kidding.

We always seem to talk about opening repertoires as if we all agree on exactly what is a repertoire, who should have a repertoire (beginners? grandmasters? 1600's like me?), how to prepare a repertoire, when and why to stick with it or sometimes vary from it, etc. But other than the somewhat common question of how to choose a repertoire, and occasional questions about whether or not to have a backup repertoire for specific types of situations/opponents, I don't recall seeing most of these other issues discussed.

So what are your thoughts on opening repertoires. Answer the 6 basic questions that apply to anything: Who, what, where, when, why, and how?