With their popularity never greater, more people are turning to polyester for the added durability it offers. For some players, poly is just too stiff, particularly in the 16 or even 17 gauges. Along with the stiffness, polys can also rob you of some power.
The answer for some may be to go thinner.
Some of the poly strings such as Babolat Pro Hurricane and Solinco Tour Bite come in a thinner 18 gauge, and in the case of the Solinco, a 19 gauge. What this does for some players is add overall playability to the strings. All things being equal, a thinner string will give you more bite on the ball, more power and better feel. This makes the poly more of a possibility for more players.
The only drawback is as you go thinner you will lose some durability. That said, a thin poly is most often more durable than many multifilament strings.
If you want some extra durability from your strings without making them feel like a board, try a thinner gauge string.