I do this too. Main monitor has sets of desktops for “primary” tasks (e.g. IDE windows) while the secondary has several “auxiliary” desktops (one for email, one for chat, one for documentation, etc).

The ability to mix and match these between monitors is seriously powerful and basically eliminates window micromanagement and seriously curbs alt/cmd-tabbing. Everything stays put as switching desktops becomes the primary form of navigation.