Using node author information in a module (efficiency)
It is a standard issue of efficiency versus convenience. You can, of course, simply join {node} and {users} tables on uid field and do it in simple select, taking just that one field you really need. And indeed it will be faster. But you will need to rebuild that part of the code if some day one of these tables will get renamed or restructured. That's why people are using CMS in the first place - to stop worrying about low level and get the job done simple and easy. Computers are cheaper than people these days.

It is possible that you will save a second of CPU time and 30kB of RAM. So what? Do you really expect so high traffic that it'll be a problem? Databases cache their results in RAM too, so it might be actually faster, overall, to always read whole node. It means one node set to cache instead of dozen sets with different fields selected. Or might not. It depends on to many variables to know, so it seems usual to considered adjusting these variables better than complicating code.