What exactly is the
/etc/init/failsafe.conf for? I have disabled the sleep timers in my failsafe.conf file which get make a faster boot up time. Are there any downsides? The only things I could come up with looking around was a this description from this link which complains that the wait time isn't high enough.
I think that  is really to small a number. You're only safeguarding against the case where a user had an entry in /etc/network/interfaces that where the device was removed or is not connected. Thats a very rare case. Increasing the timeout to 60 seconds would make it less likely to have a false positive and have rc-sysinit start early. (Ie, the case where a dhcp took 35 seconds).
Inside of the failsafe.conf file itself states
# The point here is to wait for 2 minutes before forcibly booting # the system. Anything that is in an "or" condition with 'started # failsafe' in rc-sysinit deserves consideration for mentioning in # these messages. currently only static-network-up counts for that.
I don't believe rc-sysinit depends on the network.
What purposes does