I have a "love/hate" relationship with metronomes. There is no doubt that playing alone and preparing to perform using a metronome will make you a better musician by "aligning" your personal tempo with a mechanical/electronic norm. By playing your songs to a metronome, you discover where you speed up or slow down and learn to "realign" your tempo when you go "off beat". it's all a wonderful learning experience, but it doesn't change the reality that the metronome is a "harsh mistress". The "device", as I sometimes call it, is infernal: Just when I reach the emotional climax of the song I'm working on, the "device" decides its a good time to go slower or faster (sometimes it takes on a life of its own). <sigh>
As you can see I'm conflicted about the little darling. It's helpful, but like most things electronic or mechanical, it has its limitations. it's simply not possible for a metronome to play "rubato" rhythms. The best we can hope for is to come to terms with it (and ourselves). Playing to a metronome is important in one very concrete way: recording. If there's one thing I've learned in doing my studio album, "Waiting For the Train", it is the neccessity of learning to "play nice with others". This means that, unless you are recording a solo performance, where no one else will be overdubbing you, you must play to a metronome so there will be a "unity" between yourself and other instruments. Otherwise the natural tendency to play "rubato" (with a varying tempo), will make it difficult if not impossible for others to "align" their recorded performances with yours.
The one piece of advice that I have found that truly helps when working with the infernal device, is not to accept the nature of the pinging sound most basic metronomes produce as gospel. I have found that a more drum-like "boom chuck" sound was most helpful in keeping my time because it sounded the most real. The most important practical thing I am learning in my Digital Audio Workstation application, Logic Pro X, is how to alter the sounds made by the metronome so as to eliminate the annoying and unhelpful "klopfgeist" default setting. I figure if I can find just the right sound, as I did at Wellspring Sound Studio in Acton, MA, for the metronome, the entire recording process will go that much easier and require less editing later. I have yet to find the perfect (for me) metronome sound, but I know its there and I will find it. Until then, I'll keep working on my musical "self-discipline" and carry on!
Food for thought.
Yours in DADGAD,