Many reasons to bring in your closer in say the 9th with tie game or 1 run down,,
1. hoping you score in bottom of 9th if tied ,
2. if closer has not worked in couple days they have to stay on there game thus you may see closer in 9th if your down a run.
3. this goes with number 2, say the pen has not worked very much , you bring in your closer to hold at tie or 1 run down ,,just to hold,, you may have a full or mostly full pen if you tie it , or if lucky you win it in 9th..
4. generally you do not see closer under those situations if he has worked 2 or 3 days in a row, or because he has worked couple days the coach will flat out give him the day off and not use him under any circumstance except last game year and need a win in which case even starters will be used.
5. All bull pen guys especially the set up guy and closer have to work regularly or they will lose there edge so to speak,, middle relief guys have a tendency to come in when ever as its the middle of the game and there mind set is hold for a couple innings only thus they can get pen time whenever with no effect or much effect on there arms.
hope this may clear up some thoughts you have,, np free to ask there are many good baseball guys and girls on this board to help..tks