[WAT] fun with declare @blah = varchar!

Another in my "WAT" file. (Go find it on youtube, you'll laugh and groan) 

What happens if you don't assign a length to varchar? I swear I'd learned that it became varchar(30).
Running on SQL Server 2014 SP3. Bold are the selects that are getting returned.

DECLARE @blah VARCHAR 

SET @blah = '123456' 

SELECT @blah 

DECLARE @date DATETIME=getdate() 

SELECT CONVERT(VARCHAR, @date, 112) 

SELECT @blah = CONVERT(VARCHAR, @date, 112) 

SELECT @blah 

1 

2030302

2