Something that implements a subset of Scheme is not a complete implementation of the Scheme specification, but to the extent that it is complete, mit is a Scheme dialect.

There are Scheme programs which the implementation handles, and programs developed with that incomplete implementation can be run by more complete implementations.

A Scheme programmer informed on the limits of the subset (what is not in it) implementation can jump in and start programming using what is in the subset.

A subset language can be useful to practitioners of the full language.

ThinLisp is an incomplete implementation of Common Lisp, but one which compiles to C that doesn't need garbage collection. You can develop ThinLisp programs as Common Lisp programs (with certain care). Then ThinLisp translates them to C. I think that (by default?) these translated programs don't need garbage collection.