Absolutely. While four weeks will not harm the beer (except for maybe a lager), I see no benefit to going longer than needed. But let me clarify what I mean by "needed". Old school tells us to keep the beer in the primary for 3-5 days and rack immediately after fermentation slows.
I agree that leaving the beer in the fermenter longer than those instructions is a good thing! As fermentation slows, the yeast start to go back and digest other things besides fermentable sugars, like their own waste products! Then the yeast will begin to fall out, leaving a clearer beer. I think it's important to leave the beer in the fermenter during this time. Active fermentation may take 3-5 days, then the clean up process begins.
Once the beer is at FG for a week, the processes of the yeast digesting diacetyl, etc, are pretty much over. Once the beer is clear, I see no benefit to keeping the beer in the fermenter longer.
If enough yeast is pitched to begin with (this is key!) and the fermenter is kept at the correct temperature, then there should be minimal off-flavors and the beer will require less conditioning time.
A well made beer shouldn't need a month to be drinkable, although no harm will come to it.
I have a stout that is packaged at two weeks, but it does take a total of about 5 weeks from brewday for the flavors to meld. Roasty flavors, spices, etc will take longer to really come together. But the beer doesn't have to be in the fermenter to condition.
For the vast majority of my beers, they are in the fermenter for about 2 weeks total.