From first level spell to cantrip changes a lot of the dungeon exploring game play. Minor changes in spells can change the structure of the game, and it removes some of the challenges of exploring the dark depths.
I have with interest read DMDavid’s posts on how spells can ruin adventures (Spell can ruin adventures, Spells that ruin adventures, revisited and Spells that ruin mystery and treachery), and there is no doubt that Detect Lie, Zone of Truth and Etherealness can spoil the fun of exploring a dungeon – and yet something as simple as a cantrip can, perhaps not ruin, but still limit a part of the fun of exploring a dungeon.
When exploring dungeons limited resources are a part of the challenge, and every time an effect such as a spell replaces a limited resource something is lost. Recently I have begun playing the DCC module The People of the Pit with a Dungeon Crawl Classics party and with a D&D 5th edition party, and their progress and challenges are in some places quite different.
For the DCC group carrying torches and lanterns, they have to be careful, when solving challenges spending resources – for instance they wanted to burn the bones of the physical remnants of a group of ghosts, and they had to consider how many flasks of oil, they dared spend, as they also needed the oil for their lantern. For the other party, they simply had all the light they wanted, and flasks of oil and torches could be freely spent against foes. Likewise, there was not much worry about lights going out, finding ways to cross basins, while keeping a flame burning, and into every pit is thrown a stone with a light spell in order to determine its depth.
Back in the day, when I played AD&D or D&D becmi, light was a resource, and the group’s spellcaster had to choose between using the Light spell as an offense blinding a foe or a limited light source.
I am not interested in the players tracking each and every torch, as it becomes tedious and adds no fun to the game, but using torches or lanterns, the PCs risks losing their light and being trapped in darkness, and it forces the wizard to choose and use their spells carefully (The role of light becomes obvious, when taking a look at RPGs such as Torchbearer, where light is a central part of the economy for how much can be explored).
The structural change in the game is also visible in other areas, where the simple cantrips changes the game considerably even though they have no or little use during combat.
I had the same issue when I recently ran Tomb of Horrors with a 5th edition party. Light was not an issue (but then again high-level parties do have the benefit of avoiding a lot of the usual challenges. It is a part of being a high-level character), but here another cantrip began causing problems. The spellcasters kept examining, pulling, twisting and turning everything using the Mage Hand cantrip, which being evocative of the wizard, also spared the thief for investigating a lot of objects. Gygax never wrote Tomb of Horrors to handle the new and almost limitless resources of a spellcaster with cantrips ad ritual spells
A minor change in D&D 3rd edition back in the day also took the teeth out of a wilderness campaign, I was running. The players discovered that they had easy access to a Resistance spell that lasted 24 hours and that protected them against heat and cold. This minor spell was of little use against magical fire and cold attacks, but it made traveling through a desert harmless, and the challenges of surviving the harsh climate disappeared from the game.
Next time I am starting a D&D-campaign up, I will be changing a series of spells. Light will once more be a first level spell, but also one that can be used offensively. If dungeoneering is central to the game, Mage Hand will likewise also change.