But we need to use it now so we don't waste time getting back with the bomb or getting to the shuttle.
Did I miss something? Are you saying we have the bomb?
no we dont. the idea is using it now means that when we want to get back to here of close to here we can fast travel by using the portal gun a second time. its possible that we will be in a race with another group to get to different locations. or we could even get cut off from this area at some point.
the way i look at it is we have 3 extra fusion cells. if we keep them all and dont get the power working we still need to find 5 more, otherwise there will be a fight over who gets the extra fusion cells.
Isn't the portal gun an object we picked up that will travel with us?
yes, but the way it works is you use it and then use it again. then you can jump between the 2 rooms you used it in. the pro to using it now is were close to a lot of important things and we know how to get to them from here. basically if we find the bomb or have some other reason to return to an area we have already visited having a portal here could drastically reduce travel time.