If the master client calls the first (1st)RPC and sends it to all players.
And the first (1st)RPC has a call to another (2nd)RPC within it, which it also sends to all players.
Does every player call the (2nd)RPC, several times? As many times as there are players?
Can someone please explain in simple terms, because my brain hurts 
I know tobiass is a master at photon, so I hope you don’t mind if I alert you(again :P).
@tobiass
you ask instead of testing this really quick?
Give it a try 
I have a lot of these and they seem to work. Though I’d like to know for sure.
Probably a really stupid question, how do I test it if I can’t use Debug.Log within a build?
Can you work with the UI? You could show the numbers. Or debug? You don’t have to break for every step you make. VS has breakpoints, which do something when hit (like logging) but continue to run the code (very nice to add debug logging without modifying the actual code).
Logically: When you call an RPC, all clients will execute it. So when that RPC calls another RPC, yes, all clients will fire yet another RPC. Do this a few times and you kill your network 
To fix this, I’d put checks like if(photonVew.IsMine) and stuff
right?
Yes, something like that is possible. You can call an RPC on someone else’s PhotonView. To single-out this client, everyone can check isMine, yes.