Classic Tomb Raider
In the Classic Games, the player had to press walk, jump and up to do a Swan Dive. Lara can perform a Swan Dive into water or while standing on even surfaces. Trying to do a Swan Dive elsewhere will most likely result in breaking her neck!
If you want to make a Swan Dive into a pool, make sure, there is enough space below. It is a much quicker and elegant way to get into the water.
On even terrain it can be used to get past Dart Traps, but most of the time it is quicker and easier to just run past them.
In the first sequel Rise of the Tomb Raider there are several places Lara can perform a Swan Dive. In the Geothermal Valley there are even four special platforms from where Lara can swan dive in order to complete the High Diving Challenge.
In Shadow of the Tomb Raider the High Diving Challenge is again present. Lara has to jump off four different platforms in Paititi to complete it.