Pros/Cons of changing defaultexpiry in sip.conf

What are the pros/cons of changing defaultexpiry in sip.conf?

We were receving a lot of registration timed out messages with our
VoIP provider. Occasionally, we could not receive or initiate calls for short periods of time when we were receiving these messages.

I changed defaultexpiry to 300 from the default 120.
This seemed to improve things, but did not complete resolve our
outage problem.

What can go wrong if I change defaultexpiry to 3600?

Does this mean that if we lose our Internet connection to our provider,
we may not initiate another registration for one hour?

Is there a document that describes in details the underlying semantics of changing this value, or any value in sip.conf? (I have read Van Meggelen et. all, but I need more detail)

The advantage of a lower expiery is that your server ‘checks in’ more often. If your IP changes or something like that happens, a more frequent register will make it figure that out and fix it faster.

Which provider do you have? If you use a static IP, they can probably put the IP directly into their system so it will always try your box.