“Architectural” or “Dimensional” generally means the shingle has a three dimensional design and laminated construction. In other words – more than one thickness to provide enhanced strength and aesthetic appeal. 3-tab shingles have a single layer of thickness and in general provide a lesser warranty including a lower wind rating and lower impact resistance. However if you can live with a lesser warranty, a 3-tab shingle may be a good option for those looking for a cheaper avenue.