Some will soak if conditions are too hot, or too arid, or do so just prior to shedding, or do so to seek relief from mites... and others may simply enjoy soaking.
If temps are good, if it's not too arid, if your snake is not about to shed, if your snake does not have mites, etc. ... he/she, probably, just enjoys a relaxing soak and it's nothing to be overly concerned about.