casting a spell over and over all day every minute is ridiculous. And would likely piss off your god...
But: casting that spell--as a distinct, separate act--before every check when the party can spare the 6 seconds? Totally legit.
On the first part: it's a *cantrip*, clerics can cast it at will, without needing their god to renew spell slots. See the parable about teaching someone to fish, rather than re-supplying them daily with fish. Or loaves.
On the second part: on the scale and interpretation you consider legit, Guidance is a hidden gem, on the scale of Primeval Awareness if not more so. Getting +1d4 whenever (a) you're about to attempt a stat-check task (b) you can spare six seconds (c) there aren't deterrents such as a need for silence: that's huge in a system with so few other actual plusses. If you've got +8 from stats and proficiency, Advantage will help you get a 15 or 20 or 25, but it won't ever get you to 30. Guidance might get you to 30.
There are in-setting issues and there are metagame issues.
Within the setting: If you're a god, and one of your clerics dies in the temple of Elemental Evil, and one stat check would have made the difference between survival and failure, then are you happy or unhappy that the cleric refrained from keeping Guidance active?
Within the game: does rolling d20+d4 become standard for noncombat skill checks? does the DM stop for a moment, on every stat check, to consider whether or not Guidance applies, or does trust the players to keep that in mind and roll either (d20) or (d20+d4) as appropriate?
Is a party without a cleric at a substantial disadvantage, even if they have adequate healing (paladins and other spellcasters and gallons of Healing Potion)? Is a Lore Bard at a substantial disadvantage if one of their first two Magical Secrets isn't Guidance? (Compared to other Lore Bards, of course, but even so.)
Do you allow the recasting of Dancing Lights every minute, for a party advancing into a dark cave? If so, does that create a precedent for Guidance, Friends and Resistance, in a way you consider abusive or inappropriate to the setting/story?
I am not arguing that every DM should allow 24/7 casting of Resistance, or Dancing Lights, or Guidance. (Friends has a built-in limit, because it also makes Enemies.) I am saying that Guidance, as written, may test whether DMs and players are on the same page about (a) the relationship between gods and clerics, (b) the importance of divine Guidance for heroes going on difficult, dangerous missions, (c) the pacing of gameplay, (d) the lethality level of adventuring.
Gandalf told Thorin that he'd better bring along a burglar. In 5E, either the DM nerfs Guidance as written, or Thorin would be a fool to go after Smaug without the help of someone who can cast Guidance.