What is urandom used for during boot?

I have seen some messages mentioning "random read" during the boot process, so I went and checked dmesg and found these lines:

[ 7.563793] random: init: uninitialized urandom read (12 bytes read, 48 bits of entropy available)

[ 8.614769] random: mountall: uninitialized urandom read (12 bytes read, 64 bits of entropy available)

[ 10.892396] random: lsb_release: uninitialized urandom read (24 bytes read, 96 bits of entropy available)

What are these random bits used for during boot and why?

Also, the urandom read is "uninitialized". What does this mean?

I am using Ubuntu 14.04 (kernel 4.4.0-127).