The main reason to use switching supplies is to keep weight and cost down. With cheap and reliable semiconductors becoming available, such supplies became feasible. Rectifier diodes make it easy to rectify ac lines for input to the switching power supplies. By running at a high frequency up to 100kHz and even beyond, the amount of iron and copper to make transformers is greatly reduced.
Generally switchmode supplies are used when compact size and high efficiency is important. These days they also tend to be lower cost. In a linear supply, you burn up a lot of wasted power in the regulator circuit and you need a big heavy mains frequency transformer. A switcher uses a compact high frequency transformer and the regulation is accomplished on the primary side, so the efficiency tends to be higher. The downside is increased complexity, potentially lower reliability, and sometimes the output is not as clean as a good linear supply.
Whether or not the LEDs are PWM makes no difference to the power supply.
It is easier to filter out the higher ripple frequency. If you were to use a series regulator, a smaller voltage drop across the regulating device compared with what would be required from rectified sine wave ac.
I also want to point out that switching supplies are useful for efficient charging of capacitors for pulsed lasers. If you charge a capacitor from a battery to the battery voltage, the efficiency is 50%. With proper design, the efficiency from switching supplies can be increased to over 90$%. Moreover, the low power factor seen in old capacitor charging techniques can be made to approach unity.