There's a variety of factors that decide how large a file is. Resolution, framerate, video bitrate, audio quality... Personally, I haven't ever used Bandicam so I don't know which of these you could change, but I can imagine that you can select your resolution, bitrate, audio quality, etc. But honestly, 5.40GB isn't that big IMO. I think it's nicer to edit using files of a higher bitrate and compress the entire thing afterwards when exporting. If you have plenty of space on your hard disk, I wouldn't worry about it.