There are several posts on the web this week about relationships (predecessors and successors) in project schedules. Some suggest using all the relationship to create as Cleaver a schedule as needed to represent. Another asks the question, who uses all the relationships.
These relationships include Finish to Start (FS), Start to Finish (SF), Start to Start (SS), and Finish to Finsh (FF).
Plus there can be leads and lags for each of these.
Without drawing out the pictures for each these (you can find them here), there is a very simple answer to the questions
USE ONLY FINISH TO START
That's it, Full Stop as they say in England. Don't use anything else. Here's why. First the domain we work in doesn't like it. By doesn't like it, I mean the Defense Contract Management Agency will write a Discrepancy Report (DR) for your Integrated Master Schedule if you have cleaver things like SF - 20d.
Their assessment is called the 14 Point Assessment. The guidance is found in the Earned Value Management System (EVMS) Program Analysis Pamphlet (PAP). Now every project uses Earned Value, even thoughthey should. But the advice in the PAP is good advice for all projects.
The real reason to use only FS, is all other relationship hide the natural flow of the path through the project. You can convert any of the other three releationships to a FS by simply adding a zero duration activity at the beginning or at the end of the other activity.
There are some in the community that contrive situations were SF is needed for example. This is course is exactly that - contrived. There is no actual work relationship that can be expressed with a FS.
Along with this FS advice is the use or mis-use of LEADS and LAGS. NAVAIR provides advice for this. You can have a 5 day lead or lag. On a 4 year program that is the same as ZERO days, so don't even waste your time.
Inside put a real activtiy to hold the LEAD or LAG. Here's how to do this. If you have work that has a lead or lag, this creates the opportunity for rework. Break up the work into two parts. One that send forward completed ready to use outcome and the second that carrys on.