May I just say how much I loathe line replacement??
Okay, that said it is endlessly easier than it was 5 years ago! Five years ago? I was recording on a Zoom8 and my chain had 2 other pieces of hardware in it (mixer: Mackie 402 VLZ3, and a Presonus BlueMax limiter, and despite my incredibly low noise-floor microphones, there was simply more noise. And noise? Means that when you cut, or when you replace, if you are not zoomed in on the sound to about 1/1000ths of a second, you will have a place where the noise does not line up perfectly....and you will get a click. A devastating, annoying, incledibly frustrating click.
So every. replacement. you. made. had to be done with that level of zooming in. I would about cry at how long it took.
Now I am incredibly fortunate to have a MixPre3 (an absolutely top-notch product, holy cats), and it is so so sooo quiet. Since I do not need a single other piece of hardware in my chain, there is zero added noise. Each of my mics has a noise floor 5dB and the background noise is so minimal that when I cut or replace a line, I don't have to be precise about ANYTHING - except about cutting of inhale/exhale/breath sounds :D
That said, recording line replacements, matching up the performances, matching up the placement in the stereo field and distance from the mic - that will never not be a pain in the neck :P But at least the editing is much much less painful than it used to be!