an observation... I prefer working with a live drummer, but when that's not happening I still prefer a click, specifically the UREI metronome click. I still have a UREI metronome in the rack, but don't use it as much as I used to.
 
There is just something very precise - to my ears anyway - about those clicks. And I think that's a big part of playing to a click... you need to really know the click sounds.

The other thing, again to me, is that playing to a click is playing to a metronome, even if there are tempo changes programmed in it is all about precision. Playing to a groove is more fluid, more musical if you will. A live drummer can react to the other players, and I can react to the live drummer. It is a lot different than using a drum library for me.

Now I am not complaining about drum libraries... I use them all the time because I can not always afford to get a drummer in - and space is cramped when I do - and so on<G>... and sometimes I want to write a very specific drum part.

But playing along with those tracks just doesn't work for me... go figure!

Hmmm.....to each his own I guess. 
 
It works best for me with midi drums as my rhythm guide, if I can't have a real drummer record with me.  I like to put a little extra weight into the strums that fall on accent beats and I like to anticipate the rhythmic changes before fills. 
 
Of course a real drummer is always prefered, as you say, you react to the other player.  If you have played together for a while, you anticipate each other.  A real drummer is not always possible for me.  It doesn't sit well with the wife, kids and dogs late nights and early mornings.

Forgive my dumb - what is the UREI metronome - is that  a metronome plug in?

silvercn
Forgive my dumb - what is the UREI metronome - is that  a metronome plug in?

I would say it is this rather incredible looking piece of metronome hardware.
 
 
 

As Bill says it is the sound of the click that is quite important if you are someone who likes playing to a click sound and I agree very much so too. One could probably sample that UREI click sound and place it in the same folder along with the other metronome sounds in your DAW. (Hint Bill)
 
I am very fussy as to the click sound itself. I am lucky in that the Studio One standard metronome makes a lovely click sound. I prefer it reasonably short and transient and have a slight woody quality to it. It is cool how Logic allows you to shape the click sound with a slider. For drummers a very snappy click is better.
 
As to groove and being a drummer I can say it is possible to play very precise to the click and be much tighter but one can also relax and play quite loose to it as well. As I mentioned before the click sound does not have to be on every crotchet beat either. That is where a DAW is handy because you can customise your metronome performances. Staying away from beat 1 is cool and so is clicking on the off beat. That requires some practice though so as to not turn the beat around and end up on it instead. A lot of hip hop grooves place the emphasis on the off beat so it is correct in a way to have the metronome on the off beats instead. When the metronome is away from the on beats it tends to make you play a little more relaxed around the on beats too.