Storing images in your internal drive is fine if your disk is big enough. However, most folks soon start running low on internal drives at which time they move their images to an external drive. No matter which way you go, you MUST backup those images to a drive other than the one they live on normally AND THE BACKUP YOU CAN CHOOSE WHEN LIGHTROOM EXITS DOES NOT BACK UP THE IMAGES - JUST THE CATALOG.
It is equally important to assure that backups of the catalog are also stored on a disk drive other than the one containing the in-use catalog.
iPhone Tips - iPhone External Storage for Photos and Videos – DIY in 5 Ep 80
One advantage of having the catalog on the same external drive as the images is that you can just plug that drive into another computer which has LR installed (like a laptop) and everything is there (for the most part).
If you do this and take the external drive with you when you travel, assure that you leave a current backup of that drive at home (and in some cloud storage someplace).