I like to purge my receiving vessel with CO2 before filling. If a keg, it also gets a shot of CO2 afterwards. If another carboy, it only gets the pre-fill CO2 purge.
Totally not necessary, and I didn't do this for YEARS. Once I started kegging and had a CO2 tank, then I started using CO2 as above. I also use it in conjunction with carboy caps to "push" the beer from the donor carboy (use it to start the siphon and then fill in the volume and the beer level drops (rather than letting air in).
This helps to limit any oxidation and probably doesn't matter for beer that will be consumed promptly (under 1 mo.) The extra protection of using CO2 is a good idea though for beers that will be aged longer as this will help to improve the shelf life.