If I were in a band playing the same set week in week out I'd not feel it at all necessary to have practices or rehearsals. My problem is I've got a shockingly bad memory. I have to play something A LOT to remember it to the point where I'm confident I can just play it at the drop of a hat. Dakota by the Stereophonics is probably one of the simplest songs you could play, but I couldn't tell you what the 4 (or is it 5?) notes you play on the bass are for it, I've not played it for...some time.
The thing that niggles me are the 'amateur' bands (who think they're professional) that are so cockey that they boast that they never need practices as 'they make the songs their own'. What this actually means is they can't, or can't be arsed to, play the song properly, or to properly arrange their own version. An example of this is a band I was asked to dep for recently, the drummer of which I was in a band with a few years ago. I've seen them, they play rock covers in a rock style...but because the guitarist/singer can't play any of the guitar solos they just don't bother with them. Take then Go Your Own Way by Fleetwood Mac. The drummer told me that the guitar solo part was done a capella with just bass and drum...I have no idea what that even meant. They could get away with it, to some extent, when it was an all female trio due to the large number of dirty old men and leches at venues. However, now the original bass player has left, the remaining two have had to resort to asking grotty old farts like me to play bass...I don't think the attraction value is there anymore