A past client of mine recently wrote to ask about what I think about online food trackers/apps, and which one I recommend. It's a great question, and deserved a thorough-ish answer;
For most of us tracking food intake doesn't really help with effecting health/body comp/etc, even while making people FEEL like they are improving their diet. In contrast, the work I do coaching folks on nutrition is mostly around gradually paying greater attention to specific aspects of intake, and starting to help them understand what is optimal for them/their goals. For example, if you JUST pay attention to your protein intake, and really nail minimum quantities while learning a little more about different types/viability in your body, etc. you effect a major part of your nutrition in a lasting way, without being distracted by a million details. On the other hand, with most food trackers, the premise is that fixing your diet is a process of just fixing all those details...at the same time. This is overwhelming at best and totally useless the rest of the time, at least for most busy people.
Tracking food DOES make you more aware of what you're eating, which is why food-journaling works (information is power). However, the only journaling I really have people do is taking pics of their meals and then discussing them with me. I don't use a food tracker personally, except when I want a snapshot "guess" (as you say, the estimates are not that great) of what my intake over a short-term period looks like, and even athletes I know who have extremely adherent diets rely much more on their own knowledge of intake and HABITS around eating that are in-line with their goal. I guess it boils down to, "information is power, IF you know what the information means, for your body."
Do you track your food intake? Is it helpful? Tell me more!