Mods - not sure if we want to keep the patent thing going ?
first , not a lawyer but have done these before, but its been a while but from memory (which can be foggy)
Thats the big one - but you have to file usually in multiple countries. The agreements just give you time to do it after you get one filed (ie. The USA used to be a first to invent , now its first to file - they changed it from memory - someone may know more) a number of years back - cut down on law suites, makes it simpler etc. So if you get a USA one or another country in the these agreements - you keep you filing date / date of invention - thats a big deal.
But those countries want those fees. The change from first to invent also had other implications - like when is an invention in the public domain and the time you have to register a provisional patent (the first step).
But once you get it approved say in the USA, you go from there. Also different countries have different rules. ie. the USA can take a patent if in the national interest or just if it says its top secret stuff etc (again not a lawyer - but from memory - so may be wrong).
This patent stuff is complex and when you do it can get expensive - think about $40K an application end to end with all the steps, time etc.
There are so many details in this stuff - be careful making arm chair calls.