sql group by versus distinct

Why would someone use a group by versus distinct when there are no aggregations done in the query?

Also, does someone know the group by versus distinct performance considerations in MySQL and SQL Server. I'm guessing that SQL Server has a better optimizer and they might be close to equivalent there, but in MySQL, I expect a significant performance advantage to distinct.

I'm interested in dba answers.

EDIT:

Bill's post is interesting, but not applicable. Let me be more specific...

select a, b, c 
from table x
group by a, b,c

versus

select distinct a,b,c
from table x