I rotate soaps and creams daily. My current soap rotation includes Pre de Province, Truefitt & Hill, Mitchell's, Mama Bear, and Taylor of Old Bond Street rose cream. I also have a little bit of Tabac left, but I plan not to order another puck. It's a fine soap, but I am tired of it.
What ever suits me in the morning, might change daily or run with something for a week. My rotation is down from nearly twenty soaps and creams to about ten and I see further reductions on the horizon.
I use my rotation (L'Occitane Cade, Proraso Aloe/Green Tea, Pre de Provence, Mama Bear Romance Silver Type, C&E Sandalwood, Nana June's Sandalwood/Vanilla, Vulfix Sicilian Lime Shaving Cream, QED Sandalwood/Rose) as my spirit moves me, whatever feels right.
I change my soaps daily. I always like to have something I haven't had in a while. With my rotation, I can go 2 weeks without using the same stuff and I like it that way. I guess it's what you get used to. My dad used US Palmolive lather shaving cream daily for 30 years and never wanted to change.
No rhyme or reason. Try to use something different everyday. Currently: Tabac, MWF, Arko SS, Speick SS, C&E Nomad/Sandalwood, Conks Almond, MB Coconut Lemongrass.
I tend to switch between different soaps every day and then every so often use a cream. No real system to it and usually its just a 'spur of the moment' thing.
I have 26 soaps and 12 creams at current count. I truly like being able to go whichever way the mood dictates as others have said above. I like to compare it to my father and his cigars. Properly cared for and stored, there's no reason to think I can't enjoy my "collection" well into the foreseeable future. There are plenty of vintage soaps that still perform wonderfully, so unless storage space or dire financial straits make me sell, I'll keep pretty much everything I acquire and be happy to use it years from now.