Until kaz decides that manual gears should work properly in a simulator then there is no need for the clutch. still the G27 is a much better quality overall wheel.
Why is the clutch useless?
1. No clutch slip, in GT the clutch is an on off switch and so it works nothing like an actual clutch.
2. Gears miss a lot, the game is extremely picky of how you change gear, you cannot change gear as you would in your real car, watching inside sim racing's 1hour video shows it hasn't changed, they missed more gears in 1 lap than I have missed in the entirety of the time I've been driving!
3. Paddles give an advantage, Assetto Corsa for example has a set gear change time for paddles, but if you use a clutch + h-shifter it will simply shift as fast as you shift (meaning slightly faster if you're good), but in GT paddles is always faster.
So the clutch doesn't work properly, gears miss a lot and paddles are faster. Shame but thats how it is, it was my biggest peev in GT5 and one of the things I just hoped would be glaringly obvious and fixed for GT6. Still back on point, the G27 is simply a better wheel, better still of course would be the T500 RS.