Here's some information about launch log-in queues for those that didn't experience the mess at Endwalker's release or have forgotten just how bad it was.
We don't know for certain that Dawntrail will be just as bad. The additions of the Dynamis data center for NA and the soon to open Shadow data center for EU are intended to help mitigate the wait times but that will be dependent on the number of players in those regions who choose to use those new data centers at launch.
To better understand what happens as you log in and what causes the hours long queues to form, here are links to messages from YoshiP that were posted during the Endwalker launch issues:
(initial acknowledgement of the ongoing problems)
https://na.finalfantasyxiv.com/lodes...fa3e81cf20dccf
(discussion of a specific log-in error code, auto-kick of AFK characters, and other issues)
https://na.finalfantasyxiv.com/lodes...9cad782363f25b
(discussions of additional log-in error codes and what steps SE was taking to try to prevent them from recurring)
https://na.finalfantasyxiv.com/lodes...24153ef4405c13
Note that YoshiP states in the last message that the best solution to log-in queues is the addition of new worlds for players to use to reduce the number of concurrent log-ins happening on individual worlds. We have those worlds now but it's wasted effort if there aren't enough players willing to use them.
Don't expect others on your home world to decide to use data center travel so you'll have the convenience of having a shorter wait for your home world. If you want a shorter wait time, it will be up to you to use data center travel to get it. World visit might also get you a slightly shorter wait time depending on the online population variance between your home world and the rest of the worlds in your home data center but it is unlikely get you to your home world any faster as you'd still have a wait time using world visit to get there.
Remember that when you are not on your home world, you will not have access to your retainers, FC buffs and local linkshells. You'll want to make certain you have your character inventory and chocobo saddlebags prepared with the things you'll need while doing the MSQ and other content.
When you are off your home data center, you will also lose access to FC chat and home data center cross-world linkshells (though you'll be able to join cross-world linkshells on the data center you visit without deleting any of your normal ones).
Regardless of your choice, go into Dawntrail with realistic expectations for the launch based on past expansions releases. Better to expect small problems than a smooth experience (I miss you, Shadowbringer's launch).
I hope you enjoy the adventure waiting for us.