Well, let‘s take a look at your situation. What level are your athletes or clients at? New athletes or clients probably would not benefit from percentages as much as more advanced clients, as they need to learn how to perform the lift correctly first and foremost. Second, a new client will adapt to the exercise so fast that by the next time you perform the exercise, their 1 rep max may be out of date and thus their percentages would be incorrect (if they used to bench 100lbs, but after 2 workouts they can bench 110lbs, that 60% you have them working out as now too low to cause the adaptation you are looking for).
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.