Collections and Smart Collections are probably one of Lightrooms most powerful library features. My tactic with Lightroom is to import all of my photos into a single folder, and use the Lightroom catalog to tag them with keywords and metadata, and find them via Smart Collections and searches.
A smart collection really is just a saved search. You specify the criteria you want to search by, and save the smart collection. You can quickly find any photograph that meets those criteria at any time simply by clicking on the collection. Even farther, you can nest smart collections in collection sets. This allows you to quickly find broader or narrower sets of photos in your entire library with a single click.
An example of some of the collection sets and smart collections I have:
- Landscapes (set)
- Mountains (set)
- Stormy Mountainscapes (col)
- Clear Sky Mountainscapes (col)
- Sunset/Sunrise Mountainscapes (col)
- Waterscapes (set)
- Standing (set)
- Large Bodies (col)
- Small Bodies (col)
- Flowing (set)
- Rivers (col)
- Creeks & Brooks (col)
- Waterfalls (col)
- Skyscapes (col)
- Astrophotography (set)
- Milky Way (col)
- Constellations (col)
- Nebula (col)
I have only begun to really use smart collections. My primary criteria is by keywords, as that is the easiest to filter on. You can use "fuzzy" keyword sets, by adding a single keyword rule, and separating the list of keywords by commas. This will include any photograph that has any one of those keywords. If you want an exclusive match, you can add a keyword rule more than once, with a single keyword in each. A blend of the two is possible by using multiple keyword rules that have comma-delimited lists of keywords. I recently explored them in quite a bit of detail, and they are far more powerful than just searching by keyword. You can use rating, flags, color tags, any IPTC or EXIF metadata, any camera or lens information, location data, and much, much more to build searches with.
I have about 10,000 photos, so my library is big but not huge. So far, smart collections that just use keywords has been sufficient. I have recently started rating all of my photos, so I may add or modify my smart collections to include ratings (i.e. Rivers (All) and Rivers (Best), where the 'Best' collection is 4 or 5 starred.) The possibilities are nearly endless with smart collections. The key to them is realizing that they are really saved, dynamic searches that can utilize any criteria to find any photo in your entire library almost instantly.