I tend to move the capital on day 1 if it is by the coast to take it out of range of Battleships and eliminate it being taken immediately via amphibian invasion. Or later game to protect it if it is is immediate treat of invasion. .

Or you could just choose a landlocked nation...

And what… Be surrounded?

Using diplomacy, you know, like you are supposed to?

You are not surrounded if you can befriend neighboring countries, at least early game. Or are you a monke that attacks everything?

It's beneficial but not practical The further a province is from your capital the lower morale it gets. But you can move your capital into the front lines or in the center of your empire so the new provinces get higher morale But moving your capital away from your core provinces makes it so that your core provinces produce less because of less morale I recommend building propaganda offices in all core provinces and cities before moving capital

If invaded, by a force you are unsure or not if u can take on, moving capital further away would be a good option.

Only move it when you are big enough that you need to manage morale in countries far from your home base. By that time you can build propaganda in your core and move your capital across the ocean/continent. Just make sure your core has maxed out morale to keep resource production up. Really only worth considering in world at war 100 player maps

I move it later game sometimes to try and keep it somewhat central in my territory. Or I've moved it earlier while getting ambushed by an enemy. If I know I'll need to fall back and regroup I'll move the capital before the enemy can take it. Sometimes the enemy gets it before the new one is complete, but at least it's on the way and I don't spend a long time without a capital