[mathattack]

"we would prefer to follow in this round, rather than lead it."

There are some legal reasons for this if it's a down round. If the initial investment is in one fund, and there's a down round in another, they need someone else to drive pricing so that it doesn't look like they're favoring one fund at the expense of the other. (I'm not sure why this isn't an issue during an up round)

[ganeumann]

It's often an issue in up-rounds as well.

Sometimes firms can't follow-on from a different fund even if they're following, up-round or down-round. That's why funds usually reserve money for follow-on investments.

Firms often have to go back to their LPs if they want to invest in the same company across funds.

[mathattack]

This highlights why it's important to see how VCs operate over time on issues like these. Some VCs make transition rounds easier than others.