Do you tie on fresh line to what is left or pull it off and go all new? 2 of my rigs are about 1/2 full after losing line from snagging break offs and cutting out a severe backlash. Thinking I'd tie a double uni and fill it back up. What say you?

Depends on how much the new line costs.

I don't like tying a connection knot deep in the spool. It throws off the spool balance and causes vibration during casts.

I throw a decent priced copoly, so I'm okay respooling the whole thing. If I were throwing fluoro, I'd consider leaving the old stuff on and topping off.

Mono or braid? I'll tie new line onto older braid for as long as I think it'll last.

If mono, I change mono so frequently that I'd just toss the 1/2 spool and refill with fresh line.

The only time my reels don't have old backing on them is when they're brand new.

I use backing as I'll never cast 120 yards lol so the first 30 yards or so of each reel is cheap 12-14lb mono and then either braid/flouro/good mono to fill it out. Then as I fish and return when my thumb starts feeling the small knot then I know I'm getting close to respooling. I figure saving that 30 yards or so each time means I get 2 fill ups off a 150 yd spool and with braid or higher priced flouro that's saving $$!!

Pull off some and use the rest as backing

Depends on the reel. Some of my higher end reels or smaller sized reels don't hold much line and if I'm spooling up 20lb test then its all coming off.

Yep

First, I never let my reels get half empty, when it drops more than an 1/8 inch, it's till to refill. Line is cheap. And yes, I do use backing.