Do you mean Mbps? If so, they are important because that dictates how fast your card can be read from or written to. If you'll be using it for basic image and music media (and maybe even video), then you might not have issues with that. But if you're planning on shooting video or playing movies from the SD card and this little bit of data becomes more critical. Full HD video can typically have a data rate of between 5 and 20 Mbps, which means you need a card that can achieve at least that speed. Can you record 4K video on a 10Mbps card without losing packets? Nope. Here's a little table comparing video/audio rates on Samsung phones:
4k @30fps, 48Mbps, AAC 121kbps
1080p @30fps, 17Mbps, AAC 121kbps
1080p @60fps, 28Mbps, AAC 121kbps