Microscope systems have a raw data file format that you MUST save your data in. This data file contains all of the metadata for your experiment which is important information about the system and settings that you used to acquire the images. It is critical documentation if you want to repeat the experiment the same way and many analysis software packages import features such as the size of the image in microns from that metadata. This metadata can also be extremely helpful when writing your methods section for any publication. If you maintain these original files - you can always export a TIFF if you need to later. However, if you do not save and store the data in the raw file type all of the contained metadata will be stripped from the file and PERMANENTLY LOST.

System type	File Extension
Leica	.lif
Nikon	.nd2