Do you have more information? The only issue I've heard about puberty blockers is a slight reduction in bone density over extended usage which is apparently considered negligible. I'd be interested to read a paper or medical journal indicating otherwise.
EDIT: But also to answer your question - if you think a 10 year old child might be suffering from gender dysphoria but you decide to leave it 8 years to see how things turn out, you then have to spend an enormous amount of money undoing the puberty they went through and performing various surgeries (eg mastectomy).
However if you put that child on puberty blockers and give them therapy, it should become obvious very quickly if they're just faking it for attention and they can be taken off them again.
