Flying in formation is quite a challenge, at first anyway. It never becomes something that you can perform without a lot of concentration, not well. If you relax there is a heightened risk that someone will turn towards you and catch you out.
That nearly happened today: I was just doing some checks after takeoff, taking less than half a second to look away from the leader, but when I looked back he was suddenly too close and I had to take avoiding action. I blamed the turbulence which was causing our aircraft to bounce around and to adopt bank angles not intended by the pilot. It was a (slightly) tense moment.
The weather was gorgeous, apart from the turbulence below about 3,000ft, but the sun was very low and you can see how difficult it made formation holding when the sun was behind the leader as in this shot. The next formation shot is down sun and much more pleasant to fly.
The other shot is of a tail chase, taken from the trailing aircraft. We were following the leader around the sky while he carried out various manoeuvres; it's intended to improve a pilot's handling at various speeds to maintain position and could be thought of as the precursor to air-to-air combat.