Large Full frame (35.8 x 23.8 mm) sensor Large sensor in Canon 1Ds ensures a good low light image quality compared to smaller sensor, and it also provide shallow depth of field and a nice blurry background when needed.
Large Body Even the smallest lens attached to this body will be a burden to carry everywhere with you.
1585g Carrying this weight all day may not be very comfortable for you.
Body Thickness 80mm With a thickness of 80mm,Canon 1Ds is not a pocketable camera for sure.