Of course, people can argue that one doesn't really need a metronome, and that tiny fluctuations don't matter. I guess that's okay in a live recording, as you can rely purely on band 'tightness'. But when you're recording each track seperately, you need something to go by. Hence the click track. Metronome. Whatever-the-fuck-ever.
Anyway, the biggest problems that most musicians face is recording with a click track on, as one tends to ignore the tempo and 'go with the flow', which most often leads to tempo fluctuations. This is called 'going off'. It's the worst fucking insult you can give to a musician. Only continual practise with a metronome can help, and since noone does this, they all get fucked when it comes to recording in studios etc.
The other day, i had to go and record a song in a studio, and try as i might, i couldn't do one perfect take. I kept going off and off and off, and the most disheartening sight is that of the engineer frustrated. Finally, after about 4 hours of non-stop recording, i managed to finish my song. My part of the song. Painful, but i managed.
I had to get it out of my system, sorry. I know this is a boring post. Sigh. The worst part (for you) is that this actually has helped me.