Why is --target passed when it's already the default toolchain?

[faern]

Both the Travis-CI and AppVeyor configs pass --target $TARGET/--target %TARGET% flags to cargo when building and testing. Why is this? Would it make any difference if they were removed?
At least for AppVeyor the host in the %TARGET% variable has already been configured as the default in:

- rustup-init.exe -y --default-host %TARGET% --default-toolchain %RUST_VERSION%

The reason I ask is because of this bug: rust-lang/cargo#4254
Which stops me from using the serde features = ["derive"] trick on stable Rust on Windows. So I'm thinking to remove --target from my appveyor.yml. It seems to work, just want to check if there are any factors I miss.