It depends. Dryer fabric tension holds the sheet in tight contact with dryer surfaces to increase the drying rate and uniformity of heat transfer.
On some paper machines, tensioned dryer fabrics are also used to drive the dryer cylinders. Dryer fabric tension can also reduce the cross-directional shrinkage of the paper web. There is, however, a point of diminishing return.
Excessive tension can damage the fabrics and paper machinery with no practical gain in drying capacity, drivability, sheet handling, or sheet restraint.
Fabric tensions should never exceed those recommended by the fabric supplier or the equipment manufacturer.
That said, the minimum fabric tension is about 4 pli and felt tensions in the range of 10-18 pli would normally give high drying rates, stable fabric guiding, and good machine runnability.
Slightly higher values may be required on machines with runnability components such as blow boxes and vacuum boxes.
Source: Kadant
