This is a great topic to dive into because there are logical reasons on why not to use it but it can also boil down to a personal preference. One positive to using lead-free solder, is the right in the name, lead-free. That means the hazard of developing lead poisoning is eliminated. This is not to say that lead-free solder is safe. You are still dealing with the hazard of the flux, like Rosin, that produce the inhalation hazard. This is why the use of PPE and ventilation unit or even just a fan to blow across the PCB you are working on. Standard solder has a lower melting point than lead-free solder, which makes it easier to work with than lead-free. With it having a higher melting point, it makes it much harder to work with and can take on the form of a past-like substance, resulting in a bad solder joint. Lead-free solider is also known to be more brittle and can cause tin whiskers. Tin whiskers can be very damaging to any component because it can end up connecting to pad foots together, that shouldn’t be, and causing a short between the two. A plus to lead-free is that it is also environmentally friendly. It can be a personal choice to which solder you would like to use but when it comes to sustainability and having a well soldered PCB, standard solder seems like the best choice to go with. Below is a video showing examples of the use of both.