There are quite a few posts on making reservations on the forum and you could do a search and find a lot of discussion about it. But in the west there’s a lot of public land and you’ll have a lot of opportunities to camp without them. Realize it will be dry camping, if you want hu’s you’ll be far more restricted.
If you’re just overnighting, a lot of people use Walmarts and truck stops. There’s also a lot of national forest land where you can boondock and, of course, national forest campgrounds. You can also go on the net and search free campgrounds and you’ll find some lesser know sites like city and county campgrounds. The size of you rig is a factor, the smaller the rig the more options you’ll have. But even with a big one you should have quite a few opportunities.
I never make reservations, pull a 16’ TT and almost exclusively stay on public land. But even I get caught on rare occasions and when we know where we’ll be by evening we just call ahead and find an opening in a commercial campground. And we’ve never failed to get a site. You’ll also find many other posters on the forum who travel without reservations and they do fine.
I think it mainly depends on how you like to travel. If you want the freedom to wander and can deal with having to wing it for a campsite you can travel clear across the county without reservations. If not having the security of a confirmed site would bother you, you’re probably best off to make reservations. Have a great trip either way.