They brake the spool when it is spinning rather than provide constant tension. Basically it is a centrifugal brake. If you back the tension control knob way off, you can see the difference on a cast. Agree that it is more or less fine tuning, however.
2015 Skeeter FX 21
...and down goes PhotoBucket with the new Terms of Service... I predict they will be out of business or begging for forgiveness inside a month. 6/30/2017