Tell tale signs bed tape has given up the ghost I use blue 3M Painter's tape to help with bed adhesion on my heated bed. Are there any tell tale signs which would lead me to believe I need to change the tape out?

For reference, I haven't been printing all that much, so the tape has been on there for some time. I took a look at it today and see there are some bubbles in the tape in the places where the last print I did was laid down. It appears the tape has lost some adhesion to the bed. I can run my fingers over it and it will re-stick to the bed, but is that good enough? (Obviously I'd re-clean the tape surface with isopropyl before I'd use it again, so not an issue there.) 

The last thing I want to do is waste time and materials printing when I can be more proactive, so the real question here is:

What signs might the tape be giving me it's time to change it out?
Obviously, if the tape is torn or gouged in area that you intend to print on, you will need to replace it to have a good surface. If the damage is well clear of your first layer and will not risk snagging on printer mechanisms during movement, you may disregard it.

I can't really tell you how much bubbling is acceptable. If your prints still come out in with an acceptable quality, then it's OK. If it causes defects that you don't accept, or failed prints due to a loss of adhesion, then it's not.

When I started printing, I used painters tape, and would change it every few prints. To be honest, I was not very careful about protecting the tape when removing a print, and would often damage it. I also often found it easier to just peel the tape from the print bed as a way to remove a print. I don't even think I finished a single roll of tape before I eventually switched to glass/hairspray.

I never used isopropyl or other things to clean it between prints. If you are concerned with cost and waste, I would think this would be even more than simply changing the tape frequently.