it creates sets automatically whebever you trax clip something.
This said you should always have character sets as it makes keying your character easier even f you do not touch trax, After all character sets were there way before there was a trax editor.
So basically not having craracter sets is making your animation more complex than needed. As character sets controll what the "s" key does. This saves you about half of all work ensuring right things are keyed at right time.
A clip also makes it possible for you to rebind the rig differetly after keying is done mcuh more easily.