It doesn't really make any difference whether one is a starter or a relief pitcher.
One day I was talking to my pitching coach---Ed Lopat, one of the finest anyone could ever hope to work with---and I asked him something about pitching to the hitters; I commented, "It's kind of like judo, isn't it?" He replied: "You could say that. The principle is the same---using the hitter's power against him. You make the hitters supply their own power. You take their power and turn it back against them; you give them something they can't hit. You make them get themselves out. That, in a nutshell, is what strategic pitching is all about." Lopat was a strategic pitcher, and he knew I was of the same stamp---not much on speed but with a good arsenal of breaking stuff and the control and command to go with it-- and he worked with me to help me maximize these capabilities, to take full advantage of them.
And that's where it's at. A batter is up there at the plate looking for a pitch he can drive out of the ball park---usually a fast ball, middle in---and he gets everything but, and the result is either a big fat juicy strikeout or a weak dribbler back to the mound or to the first baseman who will make the play himself. You don't have to knock yourself out to retire that batter---you let him knock himself out with a crossfire slider or a good knuckle-curve or a well-placed changeup. You can enjoy listening to said batter let loose with imprecations, invectives and cusswords that would make my computer blow up if I tried to print them. And you can think, "Aaaahhh, you're just a lousy hitter." .