No downsides except for the fact that they have said that the classic app will eventually go away, so whatever you are counting on in that might stop working some day. But no one knows when.
Meanwhile, the following might be of help (this is a clickable link)
this thread is intended only as a listing of specific differences between the two apps, not for complaints, suggestions, discussions of design philosophy, bug reports, questions about migration, joke memes or anything else. Just individual feature differences. We originally used the abbreviation STSC for “SmartThings (Samsung Connect)”, but that never caught on, so now we are calling it the V3 app since it came out with the V3 hub. The V3 app is changing rapidly, so feel free to edit this as needed.
The official knowledgebase FAQ is at the following link. Read it. https://support.smartthings.com/hc/en-us/articles/360000114006-New-SmartThings-app-FAQ
The “how to” official articles for the V3 app are at the following link:
https://support.smartthings.com/hc/en-us/categories/115…