What is the problem with UEFI? I have only installed Linux on a few computers with UEFI so far, so I don't have a great sample, but I haven't seen any problems.

What is the problem with UEFI? I have only installed Linux on a few computers with UEFI so far, so I don't have a great sample, but I haven't seen any problems. (I have heard about secure boot that cannot be turned off - how often is this the case?)