More than just the security of having water when needed I carry water as ballast.
A TT or 5er is not much more than a box of air very suceptable to wind, especially broadside wind. The weight of water down low makes for a more stable trailer whether it is in wind or going into a corner too fast. It lowers your center of gravity & does not affect fuel milage much unless doing alot of mountain driving. On the flat once the weight is moving, it takes little effort to keep it moving unless you are one of those who like to cruise at 65 plus. Then it is air resistance, not weight that is killing your milage.
