Some customers tend to think that the bigger the box better. This is not alway the case. For example we have a really big carton box that is once used and it seems to be selling very well. We alway tell customers that these big boxes are only suitable for volumetric items like bedsheets pillows and it can take weight similar to a large or medium box to be safe.
Since they are big the structural strenght of the box it not at it best as the corners of the boxes are far apart compared to a smaller box of similar material. Hence after buying the boxes, if you feel that the boxes are weak, the reason is due to what I have mentioned earlier.
Dear, Customers we do not encourage you to buy really big boxes for general moving and relocation purposes. If not sure, then go for the medium size or someting close to that size.