Most children do not need a liner in every diaper, especially when they are younger and/or still get changed at night, so if yours are not heavy wetters, it shouldn't be necessary for normal use. I only use liners at night (but then I need at least 2, sometimes 3, with my 2-year-old). Others also use liners when they know they will not be able to change as often, for instance during long car trips. Or for long naps.
Often, people will start using the diaper with no liner, and add liners only if they get leaks (which is rare) or if the diaper is completely soaked when they change their baby. Most often, when you change it, the diaper will be wet but there will still be a bit of dryness, for instance at the waist or the back. When it's all completely soaked, it's a sign that it was completely saturated and the next pee could have resulted in a leak. Plus, it can be gross to change an entirely wet diaper (usually you can manage to handle only the dry part, once you get used to it). So that's when it can be useful to add a liner.
And the snaps are nice, but not necessary. The liners stay in place well even without the snaps done, for instance in the Sandy's there are no snaps, they are on the OS mostly because the snaps were already there for the adjustment of the diaper on the smaller setting.
Hope that helps!