The most significant advantage is they have no maintenance. The light is generated directly in one fibre and connected to the output fibre. You have no moving elements inside. This system is not sensitive to vibrations or temperature variations. Only a cooling is added to the system and will demand some maintenance.
In the case of the traditional YAG laser, you have yearly maintenance to keep the laser on a stable power output level. This demands the intervention of specialized laser technicians.
The nature of the traditional laser-build cavity causes this problem. In short, a laser beam is generated in a cristal rod surrounded by a critical cooling system. The stability of laser output depends on the cooling efficiency. Water cooling systems are never entirely stable and, by nature will influence the laser output. The crystal is fixed on a super stable platform, but every nanometer of material deformation influences the laser performance again. if you get the beam out of the laser cavity, you must direct it into a 200 µ-meter fibre. This is nearly a NASA moon landing operation. Every vibration and thermal material deviation will result in less power output. In welding and cleaning processes, a +/-3%  stable output is crucial for your process. This is the main reason why fibre lasers are used in all automotive high-quality laser processes. They are the preferred tools because of their stability, low maintenance, and low energy use. A further significant difference between a fibre laser and a traditional YAG laser is the pulse duration problem. A fibre laser will generate the same pulse duration for the complete frequency range. The YAG laser will generate its own crystal material- pulse duration and will have a puls-duration variation in function of the frequency you demand. This is an extreme limitation regarding process flexibility. This means you cannot change the frequency without changing the plus duration, which is directly affecting the surface result.
The frequency of the pulses, together with the spot size, will give the maximum cleaning speed. With the puls-overlap plus energy, this is your process's main tuning point. But if the plus duration changes along the frequency, you get different heat effects on your substrate. Your process setting possibilities are limited with the YAG laser. A YAG laser finds its origin as a university development but needs a long way to be industrial reliable.
We find only  YAG solid-state crystal manufacturers like Trump and Cleanlaser.