Like Contact other Plane, Commune lets the player peek behind the curtain a bit, asking for answers their PCs might not otherwise know. Unlike the magic user spell, the risks are lower. The spell does come with its limitations though, so it's easy to see why this spell isn't a common pick.
Commune (from Cook)
Duration: 3 Turns
At fifth level, most PC clerics are probably looking at things like Raise Dead or Dispel Evil. Also the spell limits you to 1/week, three questions (less often, if the DM thinks you're overusing it), so you probably aren't memorizing it all the time. The answers are yes/no only, so phrasing is important.
The 30-minute duration seems odd, but it could be fun for a cleric to cast it ahead of time and use it to confirm information from someone as they are conversing (The Inquisition would have loved it!)
I also find it interesting that the spell description includes a special provision for doubling the number of questions once a year. Perhaps it's a specific holy day and if the cleric doesn't use the spell then, he wastes the bonus.