Here is a nice tutorial about how to loop playback in Premiere Pro.
Note the section where Ben, the editor, shows you how to make changes to the timeline as you loop. That part is an advanced tip as you can make all sorts of "on the fly" adjustments and evaluate your changes as you make them.
For me, this includes trimming and effects adjustments. If you could watch me edit here in the studio, these kinds of actions you'd observe as looping is an integrated part of my editing workflow.
Feel free to ask any questions about looping and making adjustments to the timeline as you loop.