You don't have to buy profiles. There are many factory profiles and there's rig exchange, where users can share their profiles for free.You can also profile amps (or the axe fx) yourself to get the sounds you want.
However, there are some sound engineers or pro guitar players with great amp micing skills and studio environment who capture the sounds of many amps and make great profiles. They sell them on their homepages.
Some profiles of a few of those guys are included in the factory rigs and many of those guys offer some sample profiles for free.
I suggest to check those first befoee buying anything.
Some commercial sellers offer small freebies on their sites to try, as well. I suggest that route first to try things out. And don't forget the hundreds of profiles that already come stock on the Kemper, which often gets overlooked. There are some really good profiles that come with it, especially the cleans.