If you are doing a new pattern, or a new repeat, or knitting something difficult, or especially with lace knitting life lines are a must have. It doesn't have to be anything fancy, a simple strand of any yarn any other color than what you are using in your product & the willingness to thread it thru the stitches or to learn how to thread them. Some people (like me) have needles that all you have to do is thread the base of the needle *and carefully remove stitch markers as you go* and then when you are at the end of the row it's already threaded.
Sometimes it seems that's all I'm doing is threading lifelines, but they really are life lines to keep you from messing up and tinking back any further than the repeat that you need to fix........and if you have to work on a certain section, then you can pin the stitches as you go down and pin the open stitch. Fix the error, go back & reknit up to your current row and go. (another day another time for that).