You can see from the chain pic, that the stock chain ( black ) has stretched a whole 1/2 link in only 668 miles on the bike.  This has led to the need to change to a better chain and this has what's led to it being better to use a 48 tooth rear and longer chain, than just using a 14 tooth front.  The 48 tooth sprocket with the stock 15 tooth front, gives the same drive ratio a the 14 tooth with stock rear.  But now, now more junk chain.

48 tooth rear sprocket and 118 link O ring chain for 390 Adventure