Has anyone tested the effect of allowing cantrips to be repeatedly cast between battles?

Short Version: Some characters have cantrips (or unlimited-used abilities) that they would like to have in combat, like Shillelagh. Has anyone tested or experienced methods of allowing these to be ready in advance?

Long Version: I have a player who wants to build an Arcana Cleric who uses Shillelagh, a non-concentration cantrip with a 1-minute duration, for melee combat. She would like to have it ready when combat begins for action economy (to do such other things as casting Spiritual Weapon on the first turn). She figures she can simply cast it continuously while walking around between fights.

I was considering allowing this, with a few caveats. My thoughts were:

  • Constantly casting a cantrip will give Disadvantage to be aware of surroundings, giving a -5 to Passive Perception/Investigation.
  • Since it has a Verbal component, she will be constantly emitting noise, possibly giving enemies some advance warning of the party’s approach.
  • Originally I was going to have her roll a d10 at the start of any battle to see how much time was left on the 1-minute cantrip (since it’s conveniently 10 rounds of duration), but technically she could recast it every 6 seconds to restart the timer, RAW, rather than waiting until it expired.

There are other potential factors, such as aggravating any NPCs that travel with them (imagine someone repeating the same 6 seconds of magic words over and over. ALL. DAY. LONG.), and not being able to renew it while her focus was required elsewhere (like solving a tricky puzzle, or while hiding, or while having a conversation).

Here are my questions:

  • Are there any other factors that need to be weighed, mechanically-speaking?
  • Is there any problem with my interpretation of the ability to recast it every 6 seconds?
  • Has anyone used or witnessed their own method of handling a PC constantly re-using a similar spell or ability?