I find there's a balance to be struck between convenience and granularity. If I insisted on categorising every transaction into very specific categories it would be far too much of a pain for me. So, for example, I have a big expense account called "Eating and Drinking Out". Ideally it would be great if I knew specifically what I was spending on coffee, on lunch, on beer, etc, but it would just be too much work. Likewise, I don't track my cash - I just have an expense account called "Cash Withdrawals" (unless I am withdrawing a large amount of money for a specific purpose, which I usually remember so am able to allocate it to a more specific account).
In the normal course I try to update my GnuCash once a week, which takes about half an hour on a Sunday. However I've been quite bad lately and today I'll be trying to input over a month of transactions which I'm not looking forward to...
In addition to this, I've started sampling days. Instead of recording transactions for every day, I can do something like every fifth day. This reduces precision, but it's still within a range acceptable for my purposes.
(Though it's important that it's either a systematic sample (every n days) or a random one (throw a dice each day, if it's 5 or higher, record that day). The days you pick have to be uncorrelated with the types of expenses those days, or your results will be biased.)
In the normal course I try to update my GnuCash once a week, which takes about half an hour on a Sunday. However I've been quite bad lately and today I'll be trying to input over a month of transactions which I'm not looking forward to...