While you're alive rest is never infinite. You need both enough of it and not too much, so it needs to be deliberately made to fit with all of your other things. This is important for the sake of those other things and for the sake of the rest itself.
Explicitly adding short breaks or blocks of free time into a time-plan might seem like a contradiction. The whole point of taking a break is not to be worrying about tasks and timelines and chores. But if done half-decently it reduces this worry, and improves your levels of relaxation and enjoyment. This is for multiple reasons:
If you feel you have allocated enough/comfortable time to relax, recover, or do whatever you enjoy spontaneously, without neglecting important tasks, then all the work leading up to a break is an easier burden to bare. You focus on your goals more willingly and easily knowing you are not just heading for exhaustion and more work, but have balanced your time for recovery and refreshment.
Secondly, if you are more confident, while resting, of how much time you have and that it seemed like a good amount of time when you stopped to think about your overall day, then it's easier to mostly forget about everything else for a while and just relax and enjoy yourself. If you know more clearly when the break is over you feel more clearly that it's not over yet.
It's just as risky in many cases to get too little rest, sleep, short stretching breaks, variation of activity to prevent fatigue, etc, as too much. Thinking about where and how much of these breaks to put in your plan when making it creates a good habit, and makes for plans that are more realistic and more appealing. It makes you less likely to routinely delay or pollute rest with thoughts of just doing one more thing when really you need to stop for a minute.
None of this precludes taking spontaneous breaks when you're ahead in your tasks or just really need it. Making a realistic/generous plan for your time, carefully prioritised, means you're both more likely to be ahead in the important things, and to recognise with confidence when you are ahead. This is yet another way that rest is improved with careful time-planning.
This is important because dividing your time into planned and unplanned slows down your education and training in the general art of planning your time. Once you recognise that even relaxation, leisure, breaks, sleep, etc, are improved by this art, you might embrace it more completely, and learn it more quickly.