You may have noticed that the majority of objects found in the game are stored in the inventory, and once they are used in a particular place they disappear from the inventory. This means they are of no further use and to save cluttering up the inventory and leading you on a further wild goose chase, the objects are removed. If an object remains in the inventory after you have used it this means it will have a use elsewhere too.
You will notice that in many places the floor contains a white marked area where the objects have to be used. This is not always the case. In a few rooms an object can be used anywhere within that room, so it may be wise to try to use objects occasionally in any room. Also, in at least one case, you have to use an object in one room in a specific place in order for that object to work, but the floor isn't marked to show you where. It is supposed to be an impossible mission after all.
A few objects have to be combined together to make other objects or to open certain areas. To facilitate this, upon using the first object it will be dropped where ROBOT is, and you may find the border flashes or a sound plays. You can pick it back up again without realising so be careful. Once the object has been dropped, using the second object will detect the presence of the first object and they will be used or combined. If you try to use the wrong object nothing will happen.
You may find the two objects have been replaced in the inventory with a combined object. You then have to use that object in the same place (which will drop it) so it can be used with something else.
Meanwhile, other objects do not add anything to your inventory and provide a score increase only.
The third type of object provides you with an instant power increase. You can't put them in your inventory to use later. Your battery is represented on the screen in 9 characters and there are two types of power-increasing objects to collect. One restores the battery to full, while the other gives an up-to 5 increase. If you pick them up while your battery is already full or nearly full you will have wasted them as they don't ever go up beyond 100% full.