Question: For great general fitness you should always do strength training and “cardio” separately.
Answer: Compartmentalizing metabolic-specific exercises (aerobic, anaerobic, strength, etc.) is one way to workout, but it is not the only or the most efficient strategy to achieve general health and fitness. Combining strength training and “cardio” in a vigorous circuit-like workout is not only efficient and time effective, but also impacts the metabolism in more favorable ways. And it makes more sense in the real world for those who are busy or have a real life.
The key word is general fitness — or to look great in your bathing suit without looking like a bodybuilder or like your life is all about the gym and tanning. (Sans laundry.)
If you are at about 97% of your physique potential as competitive bodybuilder (natural or steroid-using) or a high-level competitive athlete, then compartmentalization of training specificity may be considered.
But if you want to be healthy, generally fit, and look good naked (in the eye of 98% of people), then you do not have to separate strength training and “cardio.” The answer is F.