This is an answered question in the Rules Glossary section of the UA, which matches what we got in Xanathar's a few years back:
TOOL PROFICIENCY
If you have Proficiency with a tool, you can add your Proficiency Bonus to any Ability Check you make that uses that tool. If you have Proficiency in the Skill that’s also used with that check, you have Advantage on the check too. This means you can benefit from both Skill Proficiency and Tool Proficiency on the same Ability Check.
So it looks like Thieves' Tools or Sleight of Hand can be used to pick a lock, and if you are proficient in both you get Advantage.
Just like sometimes a History check or a Religion check might turn up information.
As a side note, this applies just as well to musical instruments and Perform, and other tools that have overlap. Tool proficiencies can be quite useful if you are smart about them.