Why should one use a TLP?

A feature of the design of the tethers is that they have relatively high axial stiffness (low elasticity), such that virtually all vertical motion of the platform is eliminated. This allows the platform to have the production wellheads on deck (connected directly to the subsea wells by rigid risers), instead of on the seafloor. This makes for a cheaper well completion and gives better control over the production from the oil or gas reservoir. Besides this, the minimal heave motion does not require flexible risers. The TLP is thus ideal for high maintenance wells in deep water.

The weakness of the TLP is the poor position holding in the horizontal plane. Next to that, there is the risk of ringing, and the expensive tendon attachment points on/in the seabed.

 

Summary:

Pro's Con's
Minimal heave motion Poor position holding in the horizontal plane
Production wellheads on deck Risk of ringing
Cheaper well completion and maintenance Expensive tendon attachment points
Possibility for rigid risers  
Ideal for high maintenance wells in deep water