I replace it when I get a hole or else it no longer grips the club well.
I do not play the constant glove-on, glove off game that many people play when they got close to or on the green, which I feel
1) Wastes time pulling a glove one or off;
2) Wears out the glove faster;
3) Gives me a worse grip on the club when temperatures are 90+* -- on a recent 98* day, I kept having to wipe off my bare right hand but did not have an issue with sweat effecting my grip with my gloved left hand.
4) Has no appreciable impact on my chipping or putting, whatsoever. I cannot recall ever having my putter slip or otherwise strike the ball in a manner I did not intend because of how my gloved left hand was holding on to the putter grip - my putts that I miss are because of alignment issues, underestimating or overestimating the break (I am guilty of the latter most of the time) or having the wrong speed on the putt. I suspect that this is true for 99% of the people on this board, regardless of how they talk about improved feel with bare hands.