mono backing for braid

[23cardinal]

hey guys.
never done a light <20 - 40> spinner for trout and bass<have 2> with braid. seen a lot of places say to use backing. i know for saltwater this saves us on cost, and so the line doesn't "pack" into it self too bad if some one doesn't reel in with pressure.
for freshwater, is a mono backing needed. spools only take 110 yards of 4, and 150 of 10<roughly, i forget the 40s exact> not using any crazy braids, just looking to try spider wire for hook sets

any thoughts or experience is much appreciated.