The reason woodwind instruments in general,and clarinets particular are made in sections,is because of the difficulty of maintaining dimensional stability in timber,and getting the stuff in big enough lengths in the first place.The larger the piece of timber the more likely it is to split.Now that some very good clarinets are made in various plastics,and of course ebonite,the makers continue to make the horn in bits,You must have a separate barrel for tuning,but the rest of a clarinet would be better made in one piece.The horn would be better made in a substance other than wood,now that the debate over the body material in woodwind instruments is over.I see that Yamaha is claiming in an advert that the material of the KEYS on a clarinet influence tone,or maybe it is just copy writer that has lost the plot.