From TF2 Wiki
The Instant teleport (real name unknown) was to be an alternate secondary weapon for the Engineer. It would have let him instantly teleport to his teleport exit, allowing him to have the ability to immediately return to his buildings (assuming the exit was near them) in case he needed to quickly attend to them.
The Instant teleport was cut from further development because players had the tendency to place teleport exits in spots that benefited them more than the rest of the team, breaking the idea of team gameplay. It also eliminated much of the risk of Engineers leaving their building nest alone to gather materials, creating a balance issue.
None. Provides ability for Engineer to instantly teleport to his teleport exit.