i like new strings but i almost always oil the finger boards (fretless) when changing them, so: it's a little bit of a chore/routine: if i don't plan well i end up keeping strings on longer than i might want. having said that: i probably change strings about every 4-6 months, on average. i've been playing around with TI jazz rounds on a couple of instruments: some TBer's claim they hold up "forever" --- we'll see, but so far they've held up for almost 5 months or so.
i'm with Willy-D : changing them is a must when i'm getting odd/weird harmonic issues...or when they're downright dead!
i'm with Willy-D : changing them is a must when i'm getting odd/weird harmonic issues...or when they're downright dead!