saving small data in '-v7.3' format

I am trying to figure out how '-v7.3' changes the saving method. I read in the help that it compresses files larger than 2GB. Is this bcoz default memory allocation is 2GB?

Is it unwise to use '-v7.3' to save small data? For example see below.

%code 1: file size of  "data.mat" from code 1 is ~1kB
A = [1:100];
B = {1:10};
save(['data.mat']);

%code 2: file size of  "data.mat" from code 1 is ~5kB
A = [1:100];
B = {1:10};
save(['data.mat'], '-v7.3');

My workspace has large variables (~100-200MB). When I use '-v7.3' it adds ~10-11MB. Am I doing something wrong?

Thanks