A tank without substrate and decor will be harder to look clean because there is no hiding places for the wastes. To look clean, you have to siphon off waste accumulation in circulation dead spots daily, and change mechanical filter media frequently because they get clogged up quickly from suspended waste. That said, many dealers tanks have no substrate and decor, but they also don't feed their fish to grow. But I do.
I keep large cichlids that produce a lot of waste, and I don't want a bare tank which I have to clean daily to look clean. My approach is to use HOBs to mechanically filter the water column, place a thin gravel substrate and rock decors to more effectively settle and hide the waste, and rely on weekly water change to vacuum waste accumulation in the substate and underneath rocks. There is still a lot of work because the waste won't go away until I vacuum it, but I only have to do it weekly, not daily, and my fitler media last a lot longer than a bare tank set up.
good luck. 
