The good kind of already frozen vegetables are much tastier, have better texture and have kept more of their nutrients. That is because an ordinary freezer is not nearly quick enough to preserve most vegetables.

Industrially-frozen food is frozen much faster which is good. A house freezer is not powerful (or cold) enough to freeze food sufficiently fast.

I hear that buying them already frozen is cheaper, more sanitary, and less work, but I haven't looked into it myself.