Lanefan
Victoria Rules
The goal for everybody is to have fun. "At all times" is probably stretching it.Isn't the goal for everybody to have fun at all times? I do believe that there is a level range where a fight is interesting and fun; anything below is boringly easy, everything above is frustrating. The level range can be large, but a sandbox which has both level 1 and level 20 encounters just isn't going to work.
That said, there's more types of fun than just level-appropriate fights. Sometimes the fun comes from sneaking past, or from talking one's way through, or from deciding discretion is the better part of valour and finding something else to do in a different place, or from that grand moment of realization: "Oh hell, we screwed this up! RUN!!!"
A true sandbox not only should have level <1 and level >20 encounters within it (and every level in between), in fact it must have them in order to be functionally playable. Why? Because if there's no very low level encounters then what are the low-level characters supposed to do; and if there's no very high level encounters then the high-level characters are gonna get bored in a hurry...and bored characters are dangerous, trust me on this.
And in a true sandbox it's a fact of life and death that sometimes you're going to blunder into trivially easy situations and other times you'll get in way over your heads...and sometimes those situations might come to you:
One low-level PC to another: "Yes, that's a roc flying overhead. Yes, that's an elephant in its talons. No, don't shoot it!"
Lanefan