People ask me a lot, if low resolution and file size matter with digital pictures - the answer is yes! In terms of fashion and model shots, its important to have a large good quality file as quite often it will need to be blown up to a larger size. Choose at least 6megapixels when doing a fashion shoot and choose TIFF or RAW format if possible.
Also, if you want to do any kind of editing every time you save a jpeg file it loses some quality so starting off with a small file means it can only get worse as it is played with in Photoshop. If you aren't the photographer do check with him/her the settings they are using!