If you have one, you'll want two.
If you have two, you'll want three.
If you have three...
You'll definitely want four.
I had an old summit kegerator from the late 90s. Used to just run commercial half barrels through it. When I went to homebrewing I purchased a new 3 tap tower for it. I can just barely get 3 kegs in it because the compressor is on the top in the back. I need the 1 handle kegs to go in the back and everything just squeezes in.
Anyways, yeah, 3 is good, but the beer taster I am, it's never enough. I always try to do a nice variety. I usually have my Amber on tap because it's a good every day beer. Then an IPA because it's the popular flavor and well, I like them as well. The third spot usually gets something more robust, porter, brown ale, etc. that usually take a bit longer to consume because they are more sipping beers than hard drinkers.
So I inevitably wish I had at least one more tap, to keep something lighter on hand. APA, cream ale, Hopefully lager soon. Either way, in the summer, when I have a more lawnmower style beer on tap, I wish I had room for the darker genre, to sip with a nice cigar.
And now we have a couple of local breweries that will fill cornies for you and it would be great to have some other local flavor on tap as well.
Essentially, yeah, it's an addiction. Whatever you have is never enough.