It had several things not possible in Hc, as well as somethings you can't do (strictly speaking) in Lc without reaching towards a completely different language.
For one thing, everything in SK8 is an object that can be laid down. What is the benefit in that? Well, say you didn't want to lay a stack down as your base, a field suffices. Or a button. Or a picture. You could simulate that using window shape to eliminate the block outline of a stack in Lc, but you *do * need the stack to begin with.
For another, you can directly from SK8 code to OS apis (albeit only mac os 7-9, as it doesn't run on anything newer (yet) ).
It's underpinning language was LISP, which was what the code language was as well when it initially was developed, but was changed over to Hc like language for coding. Being built in LISP, it has the ability (once I figure out what is needed) to be ported to anywhere LISP runs. Currently, I think that is everywhere, or at least, everywhere I code on.
Side benefit for LISP is that it can be compiled, Lc executes scripts within the confines of a vm like image, if my understanding of it is correct, like Squeak. LISP doesn't need to be compiled though, it can run quite happily scripted only. SK8 I believe runs like Lc, however I haven't gotten far enough to make sure that is the case yet.
A lot of tech is pretty old, Squeak for instance is ancient by comparison, however that doesn't make it worthless even today. See for instance some of these derivatives from Squeak. I actually played with SeaSide, danged if it isn't a lot of fun.