I like them because they self-seed but are easy to pull up the ones you don't want (a long taproot makes it difficult to transplant them successfully), and they bloom early in spring for a long-awaited hit of colour. When they finish their first flush of flowers, I'm going to thin them out (they're literally taking over) and deadhead the remaining ones for more blooms all summer long.
They are so pretty not only for their brilliant colour (also orange and white and pastel) but because they sway in the slightest breeze (which is one reason why ornamental grasses are so trendy these days - they add "movement").
They are very drought tolerant. Buy one pack of seeds or beg a dried seedhead from a fellow gardener, and you'll have them forever.