BYOD is popular but has some caveats - as the company grows, you wind up needing to secure ways company data can leak. It becomes necessary to plan for losses. Our computers are all encrypted and are not allowed offsite if they aren't. We also have remote-wipe capabilities, which is something a typical user isn't going to let the company install on their personal device.
We mostly allocate users laptops; a few have desktops, and most of those employees also have laptops to take home. We have allowed BYOD in the past but are now very firm on what we permit. Most users are happy to have company-supplied equipment, and I think the separation of work and personal is beneficial to most people. I like having work only on my work laptop. I only allow VPN access on a computer-by-computer basis. Admittedly we're a cloud company, so for most purposes all we need is an internet connection. The VPN gets used mostly by me to work from home, by employees who need their more powerful desktops or for me to do tech support remotely. It's not covered by an SLA but it works well for my purposes.
Sure, a lot of companies trot out the 'everyone does it this way' excuse, but there's actually a good reason for this - it works.