Riding on normal horses allows the player to move swiftly regardless of realm lag, but riding skeleton horses on realms would cause the player to move erratically, which depends on the realm lag.

Example:

When riding a regular horse on a realm, turning to another direction would cause the horse to smoothly move to the player's direction. However, doing the same on a skeleton horse would cause the horse to move to the player's direction with noticeable lag and delay.