[thaumasiotes]

> For example, what happens if they first send a probe to verify habitability? Suddenly travel times more than double.

This doesn't seem like a good idea if their method of traveling is generation ships. What would be the point?

[Retric]

One obvious consideration is to see if anyone is living there. Even just the basic economic consideration of spending a low fraction of the cost of a habitable ship to collect more data. Generation ships also implies different people will be arriving, however having a X thousands of year lifespan is another possibility. Which is kind of the thing, sharing physics is a given but biology and especially culture could be very different.