At the moment, locations are designed so that an asset is 'always' in a location and recording the time it spends there.
To get around this, we would recommend creating a location called ''onsite'' or ''in storage'' or ''not in use'' and populate this with assets.
Alternatively, you can fill a new location with assets, then delete that location to un-allocate them.
A short tutorial on bulk editing assets can be viewed below.