Mudfish Item is a set of routing rules. It makes possible to send specific traffics to a Mudfish Node. On the other hand, Full VPN mode sends whole traffics to a Mudfish Node.
Using Mudfish Items may give a change to avoid unnecessary credit leakage but sometimes it won't work at some services based on CDNs like twitch. It served on AWS.
Anyway, there's a little theoretical differences between turning Item on/off on every single time or not because if you turning on a number of Items, it'll going to near Full VPN mode so it'll more reach to limit as your maximum bandwidth but it's just choosing allow and deny to send packets to a Node so it isn't much different if you don't use as much as that.