Why would someone have a C extension but not have capos or latches on all the notes? Some extensions have just the E closer and some have only an additional latch on the D. Apart from the cost saving, some thoughts occurred to me: The resonance of the bass when the bottom is closed on Db or Eb is not as nice as when it's C, D, or E. So perhaps it's better to finger those notes that keep the string closed in those positions for any length of time. Depending on the situation, for reasons of temperament or perhaps because not everyone else in the ensemble is in tune, the tuning of the latches may not be suitable and again it might be better to finger the note and have the flexibility to tune it. I guess there is a weight saving too and there's also less mucking around opening and closing multiple latches in certain situations. I'd be interested to hear the thoughts of luthiers and those that play on extensions.