I ask this question more to satisfy my curiosity than to tend to a pressing need. But looking at the carpet in my condo (two bedroom) I don't notice any cuts in it. Was it installed as one continuous piece?
Carpet is generally sold in 12' wide rolls.
Good carpet installers use a combination of seam tape and a good stiff comb to make seams vanish.
What they do is lay down the "tape" which is actually a 4" wide strip of cloth mesh coated in wax.
They then butt the seams of the carpet up together nice and tight, and run a hot iron under the carpet between the seams (see the label on the pic above) and while the wax is still melted, press the carpet into it. Then they just comb the carpet together to hide what seam may still show.
Sounds easy but having tried it once - NEVER AGAIN. I will hire a carpet installer any day of the week.