In very simple terms (for the UK):
Outside CAS, you can use quadrantal rules for cruising levels below FL 245. (and you can do it VFR as well as IFR)
This provides at least 500ft separation against traffic going in a different general direction to you (but not against traffic going in broadly the same 90 deg sector as yourself). It therefore does not remove the need for a lookout!
Taking a compass rose and dividing it into quarters:
1) From 360 - 089 deg M: Odd levels (30/50/70/90/etc)
2) From 090 - 179 deg M: Odd +500 ft (35/55/75/95 etc)
3) From 180 - 269 deg M: Even levels (40/60/80/100 etc)
4) From 270 - 359 deg M: Even +500 ft (45/65/85/105 etc)
It is based upon your magnetic TRACK, not HEADING.
In Controlled airspace and above FL245 we use the semi-circular rule. This means the 500ft bits are removed and we use whole even or odd levels depending upon the magnetic direction.
As for whether you will be asked: It is a fairly basic bit of knowledge so I should think it might come up.