Real World Examples
As you must have noticed, the most common task relationship type is the Finish-to-Start type, which also happens to be the default type in Microsoft Project.
All the task relationships we had used in the Concert Project were Examples of Finish-to-Start relationships
Among the other task relationship types, two are used occasionally to indicate scheduling conditions which are very relevant.
Implementation of a new procedure and training for the employees on the new procedure are two tasks which can be related with a Start-to-Finish type. Although the new procedure may be ready for implementation after it has been designed, the procedure cannot be started until the employee training is completed.
Similarly, you can finish scheduling production crews only when you start receiving materials.
This relationship is used whenever we can see the possibility of overlap between tasks, though they appear to be sequential.
Thus, proof-reading for a book can be started as soon as the first few pages have been written, and we need not wait for the composition of the entire volume to be completed.
Coding for an application can be started as soon as the initial designs for some components are ready (as practiced in Agile methodology), instead of waiting for the entire design to be completed (as practiced in Waterfall methodology).
Finish-to-Finish is a very rarely used relationship. One complicated example can be the relationship between watering a garden and fertilizing the plants in the garden. As you can see, the plants have to be watered before fertilizing can start. However, the plants must be wet as long as the fertilizing process is going on. Hence we can impose a Finish-to-Finish relationship between the two tasks "Fertilize the Garden" and "Water the plants in the garden."
Another example is the relationship between the tasks "Add wiring" and "Inspect electrical". Here "Inspect electrical" cannot finish until "Add wiring" finishes. Thus, here again there is a Finish-to-Finish relationship between the two tasks. Thus, this kind of relationship, though rare, does exist between two tasks which are related to each other in such a way that one task cannot finish until the other task finishes.