Frozen veg is pretty much essential if you live alone. Roots like carrots and onions keep well. Most greens do not. Frozen cauliflower is unsuited to some recipes such as salad, but perfectly fine in a curry.

I wouldn't buy frozen carrots or cabbage, because fresh ones keep for weeks.

The freezer is a blessing. Without it, I'd have to eat tinned vegetables like in the olden days. *shudder*

Yes, but I find that frozen cauli and broc is tasteless and usually turns to mush. It's fine as a bulking agent in a strong dish like a curry, or if it is going to be masked with cheese sauce. If you want it as part of your three veg in your Sunday dinner, it's tasteless -and I prefer my veg to have a slight crunch to it, not something I can strain through a sieve.

Frozen vegetables actually have more vitamins than fresh, because they are frozen straight after picking, keeping more of the goodness in them, which slowly dissipates over time in fresh vegetables.

That said, as JJW mentions, they aren't suitable for all recipes. We use a mixture of fresh and frozen.

The only tinned veg I have are tomatoes, which I use for curries, chilli or salsas, and kidney beans which need to be cooked properly to be safe. As kidney beans are pre cooked it is not a problem.