The easy-load sleeve style album has plastic pockets that you can slip your photos into. The pockets generally are all of one size, and 4x6 is by far the most popular and common size you'll find. They do exist in other sizes, but they are less common.
Typically, you'll find two styles of plastic-pocket type albums:
Plastic sheets with pockets that fit into a 3 ring binder
Bound albums with a paper foundation, that has plastic sleeves over
If your photos are all 4x6, an easy-load plastic pocket album is a great choice. To assemble this album, you'll just slip one photo into each pocket and you're done.
The advantage of this style album is speed, and also the fact that the plastic covering over the photos does offer a level of protection from things like fingerprints and dust. The disadvantage is that the plastic pockets offer very little flexibility. If your photos are of varying sizes, or if you want to arrange a more creative layout, the pockets won't work for you.
Some pocket sleeve albums have space to write in a caption or date, and some don't. One more disadvantage of the plastic sleeves is that the available designs are somewhat limited and the plastic can make an otherwise elegant handcrafted book look a little more "ordinary," and they often don't cost any less than a more traditional scrapbook style book.