Maggie's Farm

I would arbitrarily consider any movement High Rep if you can perform over 10 in a row. With or without weights, any exercise over that begins to fall into the Calisthenics category or the Warm-up category in my book. Sure, anything can feel heavy after a while, but high-rep is a different sort of exercise unless you are a professional.

Thus if you can barely do 6 pull-ups, it's strength-building Resistance.  If you can do 20, it's more like Calisthenics. Likewise, 20 body-weight squats are Calisthenics, 4 Barbell squats to failure are Resistance.

It matters because High Rep exertions, even if reaching the breaking point, do not effectively improve strength. A useful thing about High Rep is that they do use your existing strength and help maintain. In other words, good for general fitness. Other examples are Jumping Jacks and Jump Rope which overlap Cardio and Cali categories but do not build strength.

Different sorts of muscle fibers are used. From here:

High reps develop Type 1 muscle fibers (“slow twitch”) that are endurance based and slow to fatigue.
Lower repetitions activate Type 2 muscle fibers (“fast twitch”), which have greater power but fatigue quickly.

Getting stronger is mainly about stressing and damaging those fast twitch muscle fibers. You can do High Rep deadlifts all day long and still never be able to lift a 200 lb box of rocks.

Thus the general idea is that, for strength, Low Rep with very heavy (whatever that is for you). For general fitness maintenance, High Rep Calisthenic-type exercise. For overall conditioning, I do both, plus Cardio. Almost everybody can find time for this, especially if you do it at 5 am. Why not?