Elementary question but I would like to know
if I rest every time my body is giving me some grief (even when it's just a little) will I find overall I have more energy and time to do things or will I find I spent more time resting and less time feeling really bad?
One can only reply with one's own experience on this, really, because we are all so different.
So what you need to do is experiment, and the best way to do that is to write something down. Like: "(date) rested 1/2 hour in afternoon. Felt _____afterward and rest of day was ____"
There re also different kinds of rest. So in the experimentation you ask yourself these:
Is it an actual nap where you fall asleep?
If a nap, did you set an alarm and how did that feel when it woke you up?
Did you rest by sitting down, reading something?
Did you rest by getting on a device?
How long was the rest?
And so on.
Also, the reaction to resting will be different for everyone. For some people it only makes them feel more lethargic, for others it energizes. You just have to find out which is true for you, which could be different under different circumstances.
I cannot actually nap or fall asleep in the daytime, but I rest when my body tells me to, in the way it wants at that time, and for as long as it tells me to,
if I am home and able to do that. Also for me rest never means being in front of any kind of screen, which is disruptive to me.
By doing this I am able to get things done and not pay for it with pain or fatigue later or the next day.