Like Elv13 already said: the form factor is totally different, so it won't work in any desktop enclosure or with a standard power supply.
But apart from that, server boards sometimes don't have a storage controller, no audio, only a few USB2 port. Most have onboard VGA graphics that you can't turn off, or the BIOS won't support outputting video with a different graphics card.
And then there are usually few Windows drivers and you could get into heaps of issues with (the lack of) UEFI if you want to run a desktop version of Windows.
Server boards are custom build for datacenter application and just aren't suitable for workstation use.
But apart from that, server boards sometimes don't have a storage controller, no audio, only a few USB2 port. Most have onboard VGA graphics that you can't turn off, or the BIOS won't support outputting video with a different graphics card.
And then there are usually few Windows drivers and you could get into heaps of issues with (the lack of) UEFI if you want to run a desktop version of Windows.
Server boards are custom build for datacenter application and just aren't suitable for workstation use.