I reckon that it would be an exaggeration to say that with 4 adults in a Warrior, you would have to fly on fumes, with no luggage and stark naked - but it would be uncomfortably close to the truth.
The useful load of most PA28-161's is somewhere between 830lbs and 875lbs.
Some had a MAUW of 2325lbs, others were 2440lbs. As ever, read the POH for the individual aircraft and work the W&B calculation carefully, as there is no 'one size fits all' approach to this, I'm afraid.