You still have to tune, just like an aftermarket computer. In other words, you monitor the correction and adjust the base fuel so the correction is minimal. If not, then the correction will start over every time you hit it.
PL has to be installed in the ECM at all times for it to work, since that's where the chip gets the air/fuel ratio from (as long as you have a wideband connected to PL).
The PL software itself does not need to be running, so you don't need to keep a laptop connected.
The correction speed is pretty fast. It checks and makes an adjustment about 10 times per second. If your base fuel is off, then you'll get a lean or rich spike when you first hit it, before the correction kicks in. Typically it will keep the A/F within +/-.2 of target, but you can get larger spikes on shifts sometimes.
You can download the instructions here:
http://www.turbotweak.com/turbotweak60docs.pdf
Eric