This is mainly opinionated, and since I'm young I may be wrong.
I say it's good to motivate them because then they will do a better job at their task and will make you seem like a good boss/person, especially if it's a decent pay that will keep them being able to live. With the motivation, they might even remember more things (Such as: If you work at a gas station, you remember to upsell people when a deal is going on, whereas unmotivated people forget or just don't want to do it and be lazy). It's the same effect of giving a kid a piece of candy for being good, doing chores, or getting a harder question right.