Well, either zero or all

I improvise everything, because I realized a while ago that doing that makes not one whit of difference to the quality of the games I DM.

That said, Most of my encounters are tangentially related to the plot, but... I don't know what the plot is, so some battles slip through the cracks.

As to the question you asked in your post, most of my campaigns are spent in dungeons or Cities. Travel is a few skill checks and a watch order, as far as I'm concerned.