(Sorry to resurrect an old post)
It was a lot simpler in Lightroom where you had potentially all the images you'd ever taken that you could quickly browse through, and then the collections you'd created.
Lots of people do exactly this with C1, you don't "have" to use sessions, but there are advantages of doing so, as explained in the guidance on sessions vs catalogues that was linked to earlier in the post.
Session are ideal for work that involves discrete projects and are probably more suited to professional work where work is often split into clearly identified projects e,g. The Jones's wedding 2017, or the Sarah Williams portrait June 2015. Or you might have a project that you work on over several years e.g. London Street Photography project 2014 -2018. Or at a hobby level, you may set up a project/session for things like "holiday 2017" or a project/session for all photographs of your daughter. Each project gets it's own session, which makes it easy to find, easy to archive and back up, and easy to move between computers because all files related to that project are store within a single file hierarchy within a single folder.
If, on the other hand you are something like a bird photographer, and you have thousands of bird photographs taken over several years and at several locations, a catalogue will work better as you may well want to search for every picture you have ever taken of a specific bird species, in a specific habitat, or/and showing a specific behaviour.
What you choose, depends on how you work. Some people have never used a catalogue( or sessions)and rely on labelling system folders with appropriate names, which they use to find files to open directly into Photoshop, or other editing software. Others have complex search needs and a catalogue is important. As an ex-professional photographer, sessions make a lot of sense for the project based professional work that I used to do.
For the average amateur photographer, who doesn't have a tight structure to their work, I suspect a catalogue is easier to manage than sessions. Many photographs are likely to fall into multiple categories. e.g photographs of your daughter taken during your summer holiday 2017. Do you put those photographs into a session for "daughter growing up project" or a session for your "summer holiday 2017 project".
C1 gives a lot of flexibility in letting you manage your files in a way that matches your working practices and needs, but it can take a bit of time to get your head around the options. The guidance on sessions mentioned earlier is good, as are the many webinars that Phase One have on the topic.
But, you certainly don't "have to" use sessions if a catalogue is a better match to your photography. If you do want to use them, than I think you need to think about how you might split your photography up into logical projects, where this would make it easier to find files, and not more difficult.
Cheers,
Graham
