Inspect the environment of a Process

[RudManusachi]

Would using GenServer have any disadvantages over simple Processes?

I can’t think of real disadvantages. Surely, GenServer and other OTP constructs add some overhead to bare-process as they handle more stuff for us but it’s for our own good =)
please take a look at this answer and the thread overall

When to use OTP vs 'bare' processes?

I feel the answer is probably, “not too often.” Maybe if you are building trivial tools it’s fine, but for most serious projects I believe you want to be favoring OTP construction. spawn(), send(), and receive() are basic building blocks. OTP uses them under the hood and it’s useful to learn a bit about them to help you understand the higher layers. However, you probably don’t often fire up a telnet client to check your email. You could, assuming you know the protocol commands to send, but…

Would this also allow me to inspect stuff like the mailbox, the arrival of messages, etc without adding code?

Process.info/2 could help to get the info about mailbox. Though, one thing to note, is GenServer reads messages from mailbox upon arrival and matches to one of the callbacks. So if the process is not blocked you won’t see the messages in the mailbox by checking them via Process.info/2. It’s also possible to trace the process for example with :dbg.p/2
see flag :r

r (receive) Traces the messages the process or port receives.

So it depends on what you are trying to achieve and how you build the system.