I am going to disagree. I have seen too many projects with numbers bigger than 3, some greater than 10. To me, that means the client really doesn't care about reading a proposal and looking at how freelancer can help, but more wanting to look in a phone book and taking the first 3 listed.
I will admit that since I rarely rely on invitations, I maybe really biased.
There might be differences based on the type of projects and that might change my mind about this issue, but for my group, I would rather it be limited. Maybe 3 is too small, maybe 5 is ok. Also, maybe the client could have a way to have 3 active invitations and add another if somehow one of the 3 is no longer considered. I just thing think there needs to be some limit to help focus more on getting a good freelancer for the client.
