Why would you want to cut out rice/pasta etc though - isn't that the bit that fills you up / keeps you awake / stops you being dizzy etc? If I ate a plate of cauliflower I'd have to have a proper dinner afterwards.
As Molliepops says, there are a lot of calories in bread/rice/couscous/potato etc. For myself, I like rice/couscous/potato. But in terms of allocating my daily calories, they an be inconvenient. 100g dry couscous = 367 kcal or so. That's a fair chunk of my daily allocation. (Admittedly that is a generous portion). Sometimes it annoys me slightly that I can make a spaghetti bolognaise with fairly low calorie 'mince' (I'm vegetarian) and sauce/veggies mix, but then I add the spaghetti - oh dear. Same applies for chillies/curries and rice, etc.
If the cauliflower 'rice' worked, then it'll be an option for me for some days when I want to eat something like frosted and filled chocolate cake after dinner. I'd have to save calories from elsewhere, and substituting cauliflower 'rice' for real rice would help achieve that.