A hard pressing service is an old school art that is dying. The beautician has to know how much heat to silken the hair without burning it up. If done correctly, the hair becomes very humidity resistant. However, a downside, if done enough, the hair will lose its natural curl pattern when it is wet. The hair protein loses its natural behavior. (Please see my separate article on the "effects of heat" which describes the nature of protein.)
So if you ever want to have "wash and wear" hair, then you should not seek hard pressing on a regular basis. You should embrace your natural curl pattern.
A soft press service is a healthier option, but it can be unpredictable until your hair gets trained. Getting your hair trained can take several months; otherwise, your straight look may last for about 5 minutes in high humidity weather. Can you say "instant afro?" and a feeling of "wasted time and money?"
My conclusion on naturally curly hair is to wear it curly. If you want the occassional straight look, buy a great looking wig and get it cut and styled.