That options set the maximum size of the wasm linear memory. The only difference in the binary produced is the corresponding value in the module declaration. Browsers will use this value when setting up the memory for the module. Tipically they will reserve some virtual memory equal to that amount, which should be free until actually used.
The memory allocator of cheerp will request to use more and more memory dinamically as needed, up until that limit.
So I would say that a larger than necessary value should not negatively affect your application, except maybe in 32 bits architectures (phones) when more than one wasm module is in the same tab process (since you could exaust the virtual memory).