To sum up, there seem to be 4 main approaches to XP.
1 - Per action (some variant of the standard rules)
2 - Session based
3 - Milestone based
4 - DM judgement
Different people/groups/DMs prefer different methods, and there are reasons for each. As with so much else, what really matters is that the whole group knows and is OK with whatever the approach is. If that's so, then no method is silly, pointless, or whatever. Personally, while I like per-action (and yes, I actually enjoy doing the calculations - I like doing my own taxes by hand, too.) my players prefer more milestone-based. I actually give Development Points based on engagement and character play, rather than leveling at different times.
Druss_the_legend describes a sort of hybrid of the Milestone+action system he uses. So he asked for thoughts on whether picking locks should be rewarded. It sounds like that would fit in the examples of actions that could be rewarded with XP. You could also consider the consequences of NOT rewarding XP for that, in terms of player engagement and motivation. But that's a player personality question none of us can answer.