This is a 'hand throw' which produces very fast and hard throws. It is a favourite of Neil Adams 8th Dan and British Olympic Medalist.
Here it is demonstrated as a classic combination where a 'feint' is made to the Uke's left leg forcing him to withdraw the leg thereby setting opening up the space for Tori to turn in and upsetting Uke's balance at the same time. Although the distance to fall is not as great as in some other throws, the acceleration is considerable resulting in a hard landing.
Here you can see the key components of this throw frame by frame:
In this combination, Tori enters with Tsuri Komi Goshi. Uke, in an attempt to avoid the throw tries to 'step around' and consequently opens up his body and balance for Tai Otoshi. This is an excellent example of how the theory of 'continuous attack' applies. The concept is simply that a series of throws are attempted until one is successful. The attempts have to be 'real' otherwise Uke will not react correctly. The expectation is that somewhere along the line of techniques, Uke who is reacting to Tori, will trail sufficiently far enough behind in his reactions that he will not be fast enough to correct his balance and consequently will be thrown for Ippon.