You can have multiple colonies - it's a setting somewhere that defaults to 1, but you can change it during gameplay.

I think the main reasons for moving a whole colony are resources, environment and trade with NPCs, and it's probably more an early-game thing. Harvest the good surface resources, move, and repeat until you're close to a couple good towns. Late game, once you get the deep miner, there's no limit to the materials you can mine, you can send pods to trade pretty long distances, and if you're playing mech, you can probably clean up any pollution you create.

I've only done this once because an ice age hit while i was based in a tundra zone. It was early game and I had no trees left.

Other then that I don't really see a point unless the ending your hoping to achieve requires it.

However, I recently got a mod the let's me build roads on the world map. I'm considering the idea of building Secondary "forts" near enemy bases so I can seige them. I typically avoid offensives so it may be fun.

Honestly, I find it to be something of an undercooked feature, and hope that the world outside one's home tile gets built up a bit in a future update.

You can settle new tiles for: Getting away from a threat that's too big. Infestations are a common cause for this. Cheesing resources - You can quickly grab up all the gold and silver of a map before leaving and settling a new tile. Sell at neutral bases for shock lances, horses, and food. Tomb raiding - Crack open those ancient dangers to very quickly level up your weapons and armour, as well as a consistent source of prisoners and bionics.

So new tiles can trivialise the early game gearing up and recruiting process, and at this stage there's basically no consequence to it, since each tile gives you some grace time to settle. To a lesser extent it trivialises the mid-game rush for steel, because why scan when you can go to one of the 6 adjacent tiles and load up a herd of muffalo?

So all in all I feel like settling new tiles is OP in a broken way, and I'd like to see some more consequences. Ideally, threats should be based on faction wealth, not colony wealth, and start appearing after game start, not tile settled, and some threat types should be able to chase your caravan on the world map.

You can create farming or mining colonies, if you need a lot of resources for whatever you're building. Some people simply like the challenge of running multiple colonies at the same time