I’m sad to report that I still backlash enough I seem to have fresh line always.

I typically use braid about 2 years, turn it around and use it 2 more before replacing it. Occasionally ill get into some rocks or up against some metal that will force me to turn or replace it sooner. Doesn't happen all that often because ill use a leader if I know I'm going to get into rocks.

 

I don't use straight FC or mono very much, but when I do I'm quick to change it if I feel  cover or a backlash has compromised it in any way. I did keep FC (14lb sniper) on a crankbait rod for 2 years before replacing it one time. KvD line conditioner solved all my line memory issues. 

Two or three times a year normally on the rods that get the most use, but had a couple mysterious break offs with Stren about a month ago so pulled it off and went with Steel Blue Big Game. Could've been a bad spool or just on too long. I might change out a little more often going forward. BG is cheap enough not to worry about price.

I respool often.  I retie knots and change lures a lot, and when I do I always cut off a couple or more feet of line, plus what line is used up tying the knot.  I don't like fishing with a reel half full, so some reels get new line after 3- 4 days of fishing.  Mono gets changed even if I still have a full spool because it is cheap.  Braid only gets changed when the spool runs low.  Floro gets changed every time I switch back to mono and say never again.  The Bait Monkey tried to convince me to buy more rods in order to save money on line.  If I had more rods rigged with different lures, then I wouldn't have to change lures as often, therefore I wouldn't go through as much expensive line.  I explained that investment theory to my wife.  My wife told the Bait Monkey we could move to the lake and live in a tent with all the rods, reels, and line we wanted.  I don't think she was trying to tell me she wanted to go camping.  

In 2 years or less on reels I fish a lot. Because from cutting an retying capacity goes down and casting gets shortened. I do not like any knots other than an arbor knot in my line. Maybe OCD, but, I can feel a knot in the spool when I cast.

I use straight FC on most of my baitcasters and spinning reels and change it out once/yr unless I have a nasty backlash or start to run low. I've never had any breakage issues... change more for peace of mind in case I cross paths with a giant.

3 times a month at least.