No, it is not a must.  Just suggested if you feel like you're getting inconsistant power flow between the firing pin and the positive battery connection.  Some folks swear by it, others don't use it.
*edit....it is also good to use when cleaning the terminal and firing pin during maintenance.  Again, its not necessary...just good to use on any mechanical 
mod.  I use it on my minis but only about once a month or so.