See the other comments about lambdas vs. lambda calculus, but lambdas are supposed to be for incredibly simple tasks that don't need a full function definition, things that could be done in a line or two, like simple comparisons or calling another function. This is most useful for abstractions like list filtering, mapping, folding/reducing, etc. where you usually don't need a very advanced function call.

I was always taught in classes that if your lambda needs more than just the return statement, it should probably be its own function.