All my spinning reel got backing. I use 4-8lb braid which take little to no room so backing is a must. I don’t fish a lot of brush pie so not ton of snag for me, one full spool of line should last me a few seasons, so I only use 75yds (1/2 filler spool). Another reason is once the line get low on spool I wanna be able to add more backing material to get it to full spool again (maximum casting distance), the 75yds would be a lot easier to do so compare to 150yds. Even my shallow spool still got almost 1/2 of backing. So if you plan to use #2 or #4 Fireline as mainline, you might need 2/3 spool of backing. I use line counter to make sure I got about 200’ of line. I use 4 or 6lb mono as backing using double uni knot to join. I also use plumbing tape to wrap over knot and also act my backing material if I need more.