Hello there. Well firstly speaking of Sliding, sliding is the case when you get the seat in a college but you are not satisfied with the branch you got and want to change the branch in same college. In this case you have to go with sliding option.

In the case when you are allotted a seat and you are not satisfied with that seat and want to look out for other college, then you can choose the option of float.

In both the cases, your previous seat will remain safe with you. It will only be dismissed if you choose any other seat in later stage of counseling.