I found without the tube guide the filament will become a bit brittle if you don’t print for a while ( a week or 2) and may snap in half within a few moves possibly leaving you with a terrible jam. Other than that, I agree I don’t think it’s really needed. Perhaps it also helps keep it a little bit straighter to the print head as it unwraps and untwists from the spool?
I also moved my spool up top. I downloaded and printed this one - https://www.thingiverse.com/thing:2805599. As the maker suggest, mount with 3mm T-nuts (they’re rather small T-nuts but bigger ones won’t fit inside the rails). You can get the T-nuts on Amazon. I also put the mount on both sides not just one as his picture shows. As far as the guide tube goes, I just bought the tube from Home Depot and cut to length, length being from the print head feeder to about the top of the arch of the spool. It fits the 3mm filament perfectly! The tubing is pretty cheap so you have room to mess up and isn’t super critical to get the length just right. Now, do you unspool from the top or the bottom? I’ve tried both and have gotten it to jam both ways. The filament wasn’t “loose” and eventually bound on itself and the spool, can happen in either direction. This sort of thing can happen if your filament gets unspun from the spool a bit and you manually wrap it back on; that sort of thing. I’m unspooling from the top. I don’t think a picture will really help out much but if you really want one I can oblige.