Sculpt Spells, a class feature for Evocation Wizards, says the following:

Sculpt Spells

Beginning at 2nd level, you can create pockets of relative safety within the effects of your evocation spells. When you cast an evocation spell that affects other creatures that you can see, you can choose a number of them equal to 1 + the spell’s level. The chosen creatures automatically succeed on their saving throws against the spell, and they take no damage if they would normally take half damage on a successful save. (SRD, p. 54)

So, you protect your chosen allies from your evocation spells, by letting them:

1. Automatically succeed on saving throws.


2. Take no damage, if they would normally take half damage on a successful save.

This protection feels fairly comprehensive, to the extent that in games I think we've accidentally created a houserule, lapsing into treating this rule in practice as if it actually said:

When you cast an evocation spell that affects other creatures that you can see, you can choose a number of them equal to 1 + the spell’s level. The chosen creatures are entirely unaffected by the spell.

This seems, in principle like a massive oversimplification, but I've struggled in practice to articulate what problems it might cause or think of any situations in which the literal RAW and our accidental interpretation of it would not produce exactly the same result.

So, what affect would allowing this houserule to persist have on my game? Does using the correct wording add any significance that I have missed?

This houserule makes several spells better

It's difficult to make an entire, comprehensive list of all the evocation spells that might be wrongly affected, but basically every spell that does not allow a save, or has downsides regardless of a save would be improved by your houserule.

Forcecage

You can make a forcecage large enough to fit several of your allies in, but the spell does not actually allow any saves. Therefore, anybody stuck in your forcecage is stuck there, Sculpt Spells or not.

Wall of [X]

There are a bunch of spells such as wall of stone, wall of wind, etc. that have negative effects that do not in any way allow saves. Sculpt Spells does nothing for these.

Warding wind

Everybody in the effect is deaf; no saves allowed. Every ranged attacker has disadvantage; everybody suffers from difficult terrain.

Dawn / sunburst / Other spells that make sunlight

They might automatically save to not take damage, but they're still standing in sunlight. Your drow/kobold/duergar/vampire ally is going to have a bad day.

Gust of wind

No saves allowed; several friends might suffer disadvantages.

Earth tremor

No saves allowed; difficult terrain for your allies as well.

Darkness

No amount of automatic save success is going to allow you to see in magical darkness.

All of the spells above can currently have potential negative effects on characters in the area of effect, including allies. Your houserule would totally eliminate these downsides, making those spells significantly better.

There are several changes

First of all, consider the non-damaging evocation spells, like darkness, which nonetheless are debilitating. If your allies were completely unaffected by your darkness spell, that'd be very different from what Sculpt Spell does to it normally (i.e. nothing).

Second of all, consider evocations that have side effects unrelated to their save, like gust of wind. An ally would automatically succeed at gust of wind's strength save, but would still have to spend double movement to approach you.

Thirdly, consider that some spells just don't allow a save. Spells with attack rolls are unlikely to be cast targeting your allies, but you also need to watch out for spells like Wall of Fire which has secondary damaging effects sculpt spell can't avoid.

Darkness

For starters. I know that this is not what you meant by your wording, but your rule of

When you cast an evocation spell that affects other creatures that you can see, you can choose a number of them equal to 1 + the spell’s level. The chosen creatures are entirely unaffected by the spell.

would imply that the selected creatures are not affected by the spell at all, i.e. could see through the darkness.

Earth tremor

Similar (perhaps weaker) point. Affected area can become difficult terrain, which is supposed to affect all creatures no matter the saving throw.

The list goes on

Force Cage, Ice Storm, Otiluke's Freezing Sphere, The Wall of Stone, Warding Wind

Many spells involving the elements have secondary effects that are not tied to a save; for example.

Storm Sphere:

The sphere’s space is difficult terrain...Creatures within 30 feet of the sphere have disadvantage on Wisdom (Perception) checks made to listen.

By RAW, both of these aspects should still affect the allies protected from damage by sculpt spell.