Oh, I had the bright idea to plant a bunch of Daffs in the lawn, and what a pain it was to mow around those leaves! There are hay fields surrounding the lawn, so I may stick some out there to naturalize, but these in the lawn had to go (even though it was really pretty in spring). There are a few in garden beds that I just wanted to spread out into other areas too. Some varieties do seem to bloom better when divided every few years, I find this especially true with 'Mt. Hood'. They had been blooming beautifully till this spring (the 4 year they've been here). Lots of thick foliage, but very few blooms this spring.
Some varieties never appear to require division, and will keep blooming happily regardless, like those little N.pseudonarcissus. If you have thick clumps that seem to need division, but you're not up to digging them up, I've found a quick fix way to revive them. Just take a garden fork and insert it into the clump in a few spots, and work it back and forth a bit. That loosens up the tight clusters of bulbs and seems to make them think they've got more room to grow. A few bulbs are most likely destroyed that way, but once they've gotten thick enough to need that treatment, you're not likely to notice any missing. A few times I've ran into a forgotten clump while planting something else, and started noticing that they had more blooms the next spring, that's how I stumbled upon this lazy method of reviving thick clumps.