Ah, well that would be slower. Juntioning the file from the HDD to the SSD means the file is still on the HDD and therefore dependent on it's read/write speed. My reasoning to do this was that you would install SOME files on the SSD (base game + islands) and put the less used stuff on the HDD and junction those to the SSD. You would only do this if you were restricted by available space on the SSD.
If however you have enough space on your SSD then it's always better just to install everything there! My whole Arma/ToH install is on an SSD.