Making a series of smaller works instead of one large work is the best way to improve your art.
The reason is obvious: instead of investing all your time in executing the larger image, which might already be flawed or compromised long before it is completed, you get several opportunities to get it right.
In addition to getting several more chances, you also have the benefit of looking at your previous attempt and seeing what you did wrong and would like to try differently on the next work.
That is why most of the teachers and artists who recommend “a series of smalls” also recommend that the smalls be the same composition or at least variations on the same composition or theme.
Even if your small works are different compositions, you still spend a higher percentage of your studio time making and evaluating decisions (actively learning) compared to making one large work, where the decisions are made once and most of the time is spent on execution.
This shift of focus from execution to decision making via “a series of smalls” is critical in learning the medium of mosaic because mosaic takes so much more time and effort than painting or drawing, especially when the work is large. Tiles and mortar are heavy.