One of my toilets had worked fine until few days ago. When I push
the handle, the flapper is lifted and water goes down into the
bowl. When I release the handle, the flapper should stay up for a
few seconds until most of the water has drained. But now, as soon
as I release the handle, the flapper drops down and closes the
opening. Thus, no water can go down. I have to hold the handle
down until most of the water is gone before releasing it.

I went to Home Depot to purchase a new flapper and noticed that
some of the flappers come with a float but most don't. I asked a
Home Depot employee why some flappers come with a float and some
don't, he couldn't tell me. I went to Lowe's, asked the same
question and got the same result. They don't know.

Anybody knows? Why some flappers come with a float and others
don't? What's the function of the float? If it is to hold the
flapper up, shouldn't every flapper come with a float? So, when
you change the flapper, you also change, not reuse, the float.