How many sets do I need? At least one more than I currently own, which is about 15, including plastic and magnetic sets.
Since I play out in three different type of venues: 1) in homes with large tables able to accommodate a large 2.5" board with 4 - 4.5" kings, 2) at chess club meetings, which works well with 2.125" or 2.25" boards and 3.5 - 4" kings, and 3) cafes and coffee shops with smaller tables that work best with 2" or 2.125" boards and 3 - 3.75" kings.
My 2.125" and 2.5" boards have squares only (no frames), which makes them easier to fit on smaller tables. So my large 2.5" board is the same size as a 2.25" (20") vinyl board, and the 2.125" board is the same size as a 1.875" (17") vinyl. I plan on ordering a similar 2" board later this month, which will give me a bit more space at the coffee shops.
For variety, I have about 3 or 4 wooden sets for each of the three size boards. For me, this seems to work. I'll probably sell off at least two sets before buying any more new ones.
I have been suffering from a bit of overbuying of chess sets, much like guitar players get with guitars. Its a well known phenomenon and they call it "GAS" or guitar aquisition syndrome. So, I have been asking myself, "How many chess sets does one person need?". Assuming you play in tournaments and you need at least one tournament legal set, what others would you have? A travel set for the train? A decorative set? An outdoor set so you don't have to take your good set to the park? A blitz set? An analysis set for next to the computer? A true minimalist could satisfy many of these with one good plastic set and rollup board. What do you think? If you could keep only one or two sets, what would they be? And FWIW, for some people, a decorative set is as important as any of the others so please no nasty comments about collectors.
I think the term need is relative to context...
If you wish to host a tournament, then you need as many chess sets as that would require. If you wish to make your den be dedicated to a chessic theme and want it to reflect your personality then who knows, but, if you ask whether or not a person needs a single chess set to survive, the answer is no. However, I believe you need at least one chess set in your life to say you have lived...