As a founder - I take my machine home with me. But employees keep their machine at work.
It's a tough one. Obviously keeping machines at work improves security of code etc. So I would suggest that if you do allow devs to take laptops home then VPN's/internet security/admin access/encrypted harddrives etc are all in place to ensure the companies security.
As a summary you're risking both the physical equipment as well as the IP your company has. So you need to be careful.