In the starting days of ROHS I remember we all got new Weller 80W soldering stations since the old 50W were not up to the job. I don't remember what the green multicore leadfree composition was, what I do remember that I had to relearn soldering since it neded higher temperature, more time to melt, it did not give this nice shine when it cooled down (a proof you soldered correctly and did not have a cold joint). It looked cooled down like a bad solderjoint matt and brittle. Then after two years when I needed to reprogram an old prototype board it did not work, i opened it up and almost all the solderjoints were literally corroded.
Mind you this was one of the first alloys and it sucked big time. 1+ year later on we got new lead free solder and now over 15 years later most alloys are pretty good to solder.
Still I prefer lead solder for my own stuff, just that shine

Even for reflow, it is just lower temperature, less stress on the components during reflow, less risk.