You will earn a lot of RP and SL this way. Additionally, early missions will feature weaker 'Light Vehicles' that you can easily take down.
An easy way to build up Research Points (RP) and Silver Lions (SL) is to ignore the aerial targets in favor of destroying lots of ground targets first, such as pillboxes, howitzers, AAA sites, and armored cars.
War Thunder: Sky Guardians Hints and Tips Hints