Yes. There will be significant drop in speed if you move it to external HDD.
SSD are better/faster than HDD for installing operating systems and application software because these software need to access very small but large number of files spread all over the drive. It takes more time for HDD to access these files because the platter has to rotate to get to each of these files.
Also the SATA interface is much faster than USB 3.0 interface.
Performance drops if we switch from SSD to HDD. But even more performance drops when we switch from internal HDD to external HDD.
This question can only be answered properly if we take your workflow into account. Therefore, could you expand on what sort of codes you might be running. Some background: If you apply many different small operations the SSD might affect performance significantly. It will as well when you're writing lots of data to the hard drive. However, if you have long calculations that in the end result in small data files, the will be no noticeable effect. – BramMooij – 2016-10-10T12:18:57.810