I am 6 days in on consistently wearing my heart rate monitor again. It is official that it DOES push me to go harder. I make a commitment to hit AT LEAST 500 cals every workout when I wear it.
That watch is just a little reminder during my workout that says, "Haley, you can do better than this. STEP IT UP!!!" I chose 500 because all my best workouts make it to 500+. I've had so-so workouts and super duper awesome workouts. 500 is a good middle number for me. Not asking too much but it takes effort.
Some days my workouts take me over 500+. But some days I look at it and I can tell I'm not going to quite make it. So I know I need to try harder. I start adding in plyos or heavier weights or commit to a few sprints when I'm all done with my lift. If you don't have a heart rate monitor, you won't regret getting one.