That depends on your definition of "computer". My iPhone is a fairly powerful computer, as is the 8" Samsung tablet I use. As for why to bring the latter, I use it for web browsing, email, carrying all of my reference material for the plane, flight planning, weather, in-flight ADS-B traffic display and a few other things. I could do without it, but why not have it if possible? It weighs less than a paperback, though it cost a bit more.
Fortunately my phone has an unlimited data plan and personal hotspot (thank you, O Benevolent Employer) so the lack of wifi was not a huge issue.