I consider there to be three distinct reasons to log time in aircraft:
1) To count towards minimum requirements for issue of a licence or rating
2) To be counted in duty limits
3) To be counted as overall aviation experience for employment
Any time counted towards the first has to be scrupulously within the regulations. Sometimes it is sensible to log time for the second, even though it does not meet the requirements of the first (e.g. dead-heading, or flying as a training captain in jumpseat). There are occasions too when it is sensible to log time under 3) even though it would not meet the requirements for 1) - e.g. I log time spent flying safety pilot in single-pilot jets or helicopters, even if I am not type-rated on them - they all add to my overall aviation experience.
Doing it this way is only really possible if (like me) you use an electronic logbook which allows your flight data to be presented in different ways. So if I need to present my data to an authority, I can quickly filter out all flights logged under 2 & 3. However, I can keep an eye on sensible duty limits by including 2) and 3). If presenting hours to a potential employer, I can include 1 & 3 as a representation of my overall aviation experience.