Just expanding on the information provided.
Given that a Keithley SMU is likely to see a few decades of use for perhaps a lot of different tasks, the absence of digital IO for triggering with external equipment is one likely way you will wish you had the 2612B instead of 2614B.
However, there is still the ability to coordinate the SMU action with bus trigger or sending *TRG command to it after arming it for a task.
In the attached PDF, I provide a little more detail on it.