Why is a file changed to 'UTF-8 Unicode (with BOM) text' format?

Issue

Found that /etc/hosts file was changed to the format 'UTF-8 Unicode (with BOM) text' from ASCII text.
Is this why?

$ file /etc/hosts
/etc/hosts: UTF-8 Unicode (with BOM) text, with CRLF, LF line terminators

$ cat /etc/hosts
<U+FEFF>127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4
::1         localhost localhost.localdomain localhost6 localhost6.localdomain6