I installed a laminate floor recently and had a few spots where there were open seams. The problem was that they were ugly because I could see them but more so because there was a gap that stuff could get in to.
If I rubbed my foot over it I could feel the gap. If water got in there, which would be probable because it's in my kitchen, it could wreck the floor. Dirt and small crumbs could get in there too. Another potential hazard would be if a chair, shoe or other object caught on the seam it might eventually pull up or crack off the laminate's top layer.
My solution was to fill the gaps with a color matched silicone sealer. To do so you need to run a fine line of the stuff down the seam and work it in with a finger or plastic tool. After it's worked in you need to wipe away the excess with a cloth. The silicone acts to repel any water yet remain flexible which will help in expansion/contraction. I also used a laminate floor color matched wood filler in several spots with some success also. I'm not sure if there is any real benefit to the silicone over the wood filler. They're both a form of plastic.