I do most of my reading while commuting or traveling, and typically carry an ereader (NOOK Tablet, followed by a NOOK HD) with me for that purpose. I also take my ereader with me on trips, and it's my preferred way of reading books (except textbooks, heavily illustrated books, technical manuals, or periodicals), whether at home or away from home. However, when the NOOK needs recharging, or when out and about sans the NOOK, I have no qualms about reading on my smartphone.
So...
The good (about reading on a smartphone):
- It's small, convenient to carry, and always at hand, so I can read whenever, wherever I want to
- It's got onboard reference materials and can access more online, if needed
- It can easily access my existing Calibre and audiobooks libraries, as well as sources of new material via the Internet, portable storage media, or sideloading
- The Samsung Galaxy smartphone screens are not uncomfortably small (for most reading)
- It syncs my reading progress with other devices
- It's easy to hold one-handed
- Reading on it, in conjunction with another device, nicely substitutes for flipping between pages of a DTB - especially handy for reading text passages or instructions on one device while viewing associated reference notes or illustrations (e.g., maps, images, graphs, diagrams, charts) on the other. (Big contributor to my decision to forego buying a phablet to serve as both ereader/tablet and phone)
- It's well-suited to consulting/managing one's shopping list or to following recipes when cooking
- It recharges quickly, even with a portable battery pack
The bad (about reading on a smartphone):
- The screen's too small for this to be my primary ereader or sole ereader, since I read many textbooks, technical manuals, image-laden books, and periodicals that better lend themselves to larger screens
- Unlike NickyWithNook's experience, my Samsung Galaxy S7's battery life is only so-so, when not in airplane mode
The ugly (about reading on any ereading device):
- Its vampiric dependence upon electricity (unlike a DTB), and hence the need to always carry an "electronics" kit (comprising at minimum, a cord, wall charger, and portable power pack)