lag is not as important as getting the shaft leaning forward at impact. Lag does contribute to this however. More importantly, I think you are referring to the release point of the lag.
releasing early can cause the bottom of the swing to go further back, resulting in fats and thins. Although it is still possible to strike consistently with a relatively early release. I do...
release point of lag is not the magic bullet to distance than people think it is though - it is not going to add 20 MPH to your swing speed by holding the angle for as long as possible. The majority of distance increases from this come from the fact the clubhead comes into the ball with less loft, projecting it forwards more, rather than upwards. The amount of total wrist set has more to do with speed than where you release it.
So my advice is - if you suffer with fats and thins, focus more on getting the club leaning forwards at impact rather than lag itself. Although lag contributes, you can have very little lag and have the clubhead leaning forwards at impact.
if your problem is speed (which by the sounds of your post it is not) then focus on maximising the amount of wrist cock in downswing, but don't worry so much about the release point of the lag.