You’ve probably read or heard somewhere that toning (using smaller weights for higher reps) doesn’t work and is a complete waste of your time.
While I’m not here to totally disagree (if you truly want to build muscle, you will need to lift heavy things) I do want to point out that telling somebody who’s overweight or not comfortable yet with harder workouts… can be a bit discouraging.  Here’s a really well put comment when it comes to telling people that toning tighten and firm workouts don’t work.
Making fun of people who do toning exercises is not helpful, and claiming that they will produce no results at all is lying. Be encouraging instead of demeaning. – Reddit
It’s similar in the misguided thinking.  While the 2nd is way more efficient, it might discourage somebody who’s really need to put their big toe in the water and start to wade in deeper.
That being said, I am not a believer in toning exercises.  You should lift a weight that makes it hard to do, encouraging your body to change.  If that means lifting the pink dumbbells to 20-30 reps where it’s impossible to complete another repetition under your own power, it sure beats lifting that same dumbbells for the same repetitions with ease.
There’s a very good study that tackles the question, does light load training build muscle in experienced lifters?  If you read it carefully, you’ll still see the repetitions are done at a higher range but the weight used pushed the person to fail which means it wasn’t that light.  It was just much lighter than you’d typically use at a much lower rep range.
Thus, high rep, heavy weight training can build muscle.  It’s not as easy as it sounds.
The point being, you build muscle, maintain muscle or you don’t build it.  The concept of toning is technically misleading.
In many cases, people have done what we think are toning exercises and it turns out they build up some muscle, burned off the fat and looked better than before.  Mainly because something is better than nothing.  And when they did what most of us “meatheads” consider very light weight, it was relatively difficult for them and they did it in a fashion that pushed their limitations.  In essence…
They thought they were just toning but in fact, they were building some muscle and burning fat!
Maybe not as efficiently as they could with a lower repetition scheme and heavier weight but it still worked and allowed them to feel more at ease. That’s not to say you should dump the concept of lifting heavy things!  You should strive for that for numerous other reasons.
The bottom line is that toning is just inefficient weight lifting but it can and does work if the work is done to a point that is hard for the client.