Hugo Kornelis (2/1/2016)
In these two cases the impact is only performance. However there are other cases where the implicit conversions can impact the usability of an index, or even change a very efficient remote query to a terrible one (speaking from personal experience). So my advice is to stick to the generic best practice to avoid all implicit conversions, and to minimize the explicit conversions to the bare minimum.
Yeah, I've had that personal experience as well. Once you run it out to 1M rows or more, that performance impact is felt more and more. Please listen to Hugo's advice here and just avoid implicit conversions everywhere.