You might be interested in threads from the FAQ section on "The Holy Roman Empire and Centralization":
Centralization and the Holy Roman Empire
-o- "Was the Holy Roman Empire always very descentralized , or did it become more descentralized with the passage of time? Were Medieval Kingdoms, such as France before the 100 years War, as descentralized as HRE?" (11 comments | 5 months old)
-o- "Why did the Holy Roman Empire have such a decentralized government?" (6 comments | 2 years old)
-o- "How did the Holy Roman Empire become so decentralized?" (5 comments | 2 year old)
-o- "Did the Holy Roman Empire fragment from its original state, or did it just remain fragmented while other states centralized?" (4 comments | 1 year old)
-o- "I'm confused on The Holy Roman Empire" (6 comments | 2 years old)
-o- "How did the German Principalities of the Holy Roman Empire obtain such crazy borders? How were they administrated? What did they mean for a common person or even wealthy merchant in the Holy Roman Empire?" (76 comments | 4 months old)
Comparing the Kingdom of France and the Holy Roman Empire
-o- "Why did the Holy Roman Empire become a decentralized patchwork of states while France became a centralized, unified kingdom?" (43 comments | 6 months old)
-o- "Why did France (West Francia) end up more unified than the rest of the Holy Roman Empire (East Francia)?" (12 comments | 1 year old)
-o- "Why did the Holy Roman Empire end up so decentralised in the first place?" (5 comments | 1 year old)
-o- "Why did the French kingdom become much more centralized than the Holy Roman Empire?" (7 comments | 1 year old)
##Followup Questions
If, after looking through the above threads, there are major questions that have been left unanswered or specific topics given insufficient detail, feel free to ask followup questions. Liberal quoting from these threads are encouraged to both allow for clearer answers and to prevent users from wasting time repeating points already addressed.
The following users are flaired on the topic and/or have answered questions on it in the past, and would likely be able to answer these followup questions:
-o- /u/butter_milk
-o- /u/HenkieVV
-o- /u/stefan2494
Follow-up question: Was the HRE ever centralized?