I have used an app a few times with #3. i always have my phone so i found it easier to use an app this time. I used a diary for #1, but had no toddlers to escape with the pen/diary or scribble on it/take pages etc.

I wanted to track feeds for a couple of days, because i didn't think she was feeding effectively or often and so i wanted an idea of length of feeds and how many in a day. I found out she was having more feeds than i thought she was, which was reassuring.

I tracked quite a lot of DDs (#1) habits, none of DSs (#2) and have done intermittent tracking of feeds with DD (#3). i think it has its place, but don't stress if its not your thing.