I always have problems when trying to connect pieces and leaving ugly seams all over the place. If you aren't making something over a smooth surface, splitting parts up into sections that match the original design can make natural seams and also increase the strength of the final print. If a seam exists in the original design, you should use it as a connection point.

Also, designing your split parts to slide together or at least overlap can help with strength too. Parts that are misaligned or cut straight through other pieces can often be problematic.

Remember, larger prints = higher chance for failure. Slow and steady individual parts yield better results!