I formed the HRE around 1525, and if I would have had the idea before, sooner, which I will do in my next game. The last four phases were passed in less than six months simply releasing countries as vassals, with the bonus of giving them catholicism.
The reasons to do that were mainly two:
a. I was tired of not having money, nor manpower, so I imagined that annexing all HRE was an interesting idea to solve this problem: forming it trippled my monthly manpower, and gave me an increase of +80 monthly ducats with 100 more divisions, allowing me to hire 3 stars advisors, instead of just one star.
b. I lost +15% income, legitimacy +1 bonus, -2% construction, etc. Very few benefits.
My point of view is that the new 1.6.1 conditions generate a situation in which your only view is to form HRE as soon as possible.
The reasons to do that were mainly two:
a. I was tired of not having money, nor manpower, so I imagined that annexing all HRE was an interesting idea to solve this problem: forming it trippled my monthly manpower, and gave me an increase of +80 monthly ducats with 100 more divisions, allowing me to hire 3 stars advisors, instead of just one star.
b. I lost +15% income, legitimacy +1 bonus, -2% construction, etc. Very few benefits.
My point of view is that the new 1.6.1 conditions generate a situation in which your only view is to form HRE as soon as possible.