Appart from the building regs specification on the size and positioning of notches and holes in joists is there a best practice on what to use? Is it just the case that notches are used in place of holes due to the cable positioning being outside that prescribed for holes. Are there any issues with not clipping cables under floor boards? I say this as when for instance you install down lights it seems prudent to have a fair bit of slack left for future work / fittings etc.