I can think of one advantage...It keeps me in a job.
I can understand asking for help on a forum like this, but please please please, at least attempt the question yourself, at least read your textbook or notes you've got.
You have access to the internet, load up google.com and type in "PLC Industrial Automation Advantages" and see how many pop up. The internet is meant to be there so people can find information about anything, use it.
Almost any generic question and most specific ones can be answered using the internet. I assumed this Forum was for people with specific problems, for discussion about PLCs in general and things along those lines.
If you come back with more specific questions then i guess many more people will help.
For example "Why is advantage A an advantage if blah blah..."