Context matters a lot when you see programming advice and discussion. For example, consider a program keeping track of whether an item has been viewed or not. One may argue that state should be kept as small as possible: if the information you need is a single bit, use a single bit, no more. Pack your bits if you have to! Another may argue that we are not only interested in this one bit, but down the line also interested when an item was viewed. So really what you want is not a bit, but a timestamp.
Both perspectives make sense. When you have are manipulating data in an application, the single bit may be preferable on account of its economy. And should you become interested in when the item was viewed, the change you make to your codebase is probably pretty limited. You will probably only deal with the timestamp in the place where it is relevant, and use the single bit everywhere else.
However, when you have a big database that other people are going to use for analytics, new application development, and god-knows-what, it makes sense to store the timestamp rather than the bit! Economy avails us little here (usually): the database is big, the number of rows is limited (what's a couple million among friends, eh?), and evolving the schema is painful. Here I think it makes sense to store the timestamp as representation that's closer to reality and more useful to others. I certainly have never regretted using a timestamp rather than a bit in a database (yet), but I do regret cases where I used a bit rather than a timestamp.
Another argument I would make is in the case you are using a high-level language like Python.
In Python, trying to twiddle the bits is more or less useless: pretty much everything is a PyObject, which is relatively bulky and will not perform well in any case, so I suspect the bit approach will not yield much better performance than the timestamp approach.
Rather, look closely at whether you need the information at all.
Nothing at all is more economical than even a single bit!
So context matters. A developer building databases will think very differently from a developer using database.
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