As a tutu maker myself, I prefer the unsewn look. I could upgrade to sewn tutus but as others stated it is a lil more time consuming and why fix something that isn't broke!
I have a special technique I use to where they can't be untied. I get all my tulle from nashvillewraps.com.
I take pride in having the softest tulle. Its a definate must for the newborn/infant tutus.
The tied tutus come out way more poofy than others in my opinion!