The main differences between the two are the set-up position and specificity to pulling movements. In the Pendlay row, you’ll set up with your back roughly parallel to the floor. This makes it much more difficult to assume a proper start position than with other types of rows.
The Pendlay row also has great application to movements like deadlifts and cleans. That’s because the barbell starts from a static position on the floor. You’ll pull it upward without allowing your hips to move up or down. This reinforces a strong setup and start position for those more advanced movements.