Do you roll dice when a saving throw's result is an automatic success/failure?

Question

There are several features such as the bones of the earth spell which states:

[...] If a pillar is created under a creature, that creature must succeed on a Dexterity saving throw or be lifted by the pillar. A creature can choose to fail the save...

The Sorcerer's Careful Spell Metamagic option which states:

When you cast a spell that forces other creatures to make a saving throw, you can protect some of those creatures from the spell’s full force. [...] A chosen creature automatically succeeds on its saving throw against the spell.

And the compulsion spell which states:

[...] A target automatically succeeds on this saving throw if it can’t be charmed...

In cases like these does the target creature roll dice at all? Have they even made a saving throw?

Answer 1

No dice are rolled.

You are still making a saving throw, it's just that it works differently than your normal dice rolling.

This is because if you automatically succeed or fail on a roll, then there are no dice that need to be rolled.

The DMG generally covers this idea on page 237:

When a player wants to do something, it’s often appropriate to let the attempt succeed without a roll or a reference to the character’s ability scores. For example, a character doesn’t normally need to make a Dexterity check to walk across an empty room or a Charisma check to order a mug of ale. Only call for a roll if there is a meaningful consequence for failure.

When deciding whether to use a roll, ask yourself two questions:

• Is a task so easy and so free of conflict and stress that there should be no chance of failure?
• Is a task so inappropriate or impossible — such as hitting the moon with an arrow — that it can’t work?

If the answer to both of these questions is no, some kind of roll is appropriate.

Unless the saving throw has a qualifier for failing or succeeding by a certain value, then there is no reason to roll because the actual value doesn't matter - only success or failure matters and that's been predetermined.

Because of that, there is no opportunity to roll when the numerical result doesn't matter.

If you really wanted?

I mean, I guess if you really wanted you could say that you roll, but whatever the result is, you get the predetermined result.

Answer 2

As NautArch said, there is no need.

One thing I want to add for why it is not useful to roll is that there are no special numbers that will magically change the results of your roll.

When you do an attack, a natural 1 is an automatic failure (in the old days you would even roll a fumble die in this case) and a natural 20 (at times 19) is an automatic success and you do double the damages.

I think that's the main source of confusion. The saving throws do not offer any special cases, so rolling whatever will always have the same result, no matter what.