When a VC or other mainline investor says they will "follow," it means:
1) We like the proposition, we can bring something to the deal, it fits our profile, but...
2) we don't have the immediate expertise to set the valuation or we don't want to spend our time negotiating with the founders/inventors.
It's often a simple matter of bandwidth. Deal looks good. We'd be interested in coming in. Need a lead, though, to take care of the messy stuff. Leads investors come in more easily if there are followers ready to round out their investment. Just understand the roles and find the right players for each.