Seams are not invisible. Everything has a seam, your clothing, sofa, wall paper, sheet good vinyl flooring. Your carpet choice is a factor in how much a seam shows berbers and flat velvet piles will show seams the most. Sisal for sure. Some high pile plush carpets to a degree, the best to hide seams are shags and high twists as the pile “falls over” on itself to hide the join. Pattern carpet can fool the eye with seams but can jump out if the pattern is not matched correctly. Seams are not a problem in England or Europe, 27″ wide goods are the normal where the standard for U.S. is 12′ wide or 15′. Some imported wools can be 13’6″ but rare. Americans are the most “Seamaphobic” but check out some euro design magazines and you will see 27″ wide stripes in a room.