The next thing to look at, what are the goals of the client? Many clients like personal trainers simply to help them work out, no specific goals but general overall fitness. For these clients, percentages are probably unnecessary as you as the trainer can monitor their intensity and effort by watching. If it is an athlete preparing for their sports, intensities will give you a great guideline to go by and allow you to accurately pick a weight for their work sets that will increase their potential for strength.
Microsoft Excel is a fantastic tool for analyzing scientific data. Microsoft Word is a fantastic tool for writing up scientific research. So surely Microsoft Office is the only software a scientist would ever require beyond that associated with specialist scientific apparatus? Unfortunately, that has never been the case and most university researchers would identify one big problem with the Office suite and that is why it‘s always been difficult to present formulas in Word and Excel. Even when you type a simple fraction like 3/5, it gets presented on a single line. As for Greek symbols like pi...well, that would mean many hours wasted trawling through Excel‘s Insert Symbol menu.