I use it all the time - it's the killer feature of google photos. The premise is that if you come back from vacation with 300 photos, it's unlikely that you (the average non photography-nerd user) are going to sit there and tag them all. If in a few years you want to find "that photo of me you took on the beach in north carolina", with a quick search you can.

There are annoying limitations though, probably because the original team moved on and it's in maintenance stage. Using my example above, google photos has no idea what the "outer banks" are (which is where the beach photos were taken in north carolina) and returns no results. It also has trouble parsing out entities from search terms, so "north carolina beach maggie" isn't going to find pictures of Maggie on the beach in North Carolina (which you'd think they could really fix given that, well, they're google). Finally, there's no way (that I know of) to jump from search results to your full timeline; let's say that "north carolina beach" gets me a bunch of beach pictures from January 2015 (yeah, it was cold), but doesn't have _the_ picture from the trip that I know I want - there's no direct way to click to January 2015 from the results, which really sucks. (Instead you have to go back out of results and use their fiddly scroll to get there.)