This has no effect on the cigars. many members on here have coolers stuffed full of cigars from diffrent regions for upwards of 10 years or more. No harm there.
If they are touching, it will cause their flavors to blend, as oils from one mix to the other and are reabsorbed. Over extremely long periods of time, even having them in the same humidor will cause a tiny amount of blending. For instance if you put a really mild connecticut in with a lot of strong maduros, the connecticut will be slightly stronger.
Additionally, the less your humidity and temp levels vary, the less this happens. Whereas if you see large swings in your temp and/or humidity you will get a lot of flavor blending (though this is probably the least of your worries if you have large swings in temp and/or humidity).
Flavor blending mostly happens when two or more cigars lose and then regain humidity. If the temp rises and/or the humidity drops, the cigars will lose oil and moisture, as the cigars get back to a good humidity level and/or temp they will reabsorb oils and moisture, which will now be a mingling of what the other cigars released.
If you have a perfectly stable 70/70 with little to no variance, as long as different wrappers aren't touching, almost no appreciable flavor blending will occur.
On the flip side, sometimes you want flavor blending, mostly within a box of the same cigar. For instance, if you buy a slightly less than premium cigar, a lot of times the biggest problem is that there is a good amount of variance between the sticks (mostly because they were rushed to production and didn't get to bond in a shed together). If you leave them in the box, with their wrappers touching, eventually the smoke will be a lot more consistent from stick to stick. This is why if I have a box that I'm storing and they're cello wrapped I will remove all the cello, to speed along the blending process. If I have a bunch of singles that I'm storing near one another, I will leave the cello, or if the cigar didn't have cello, try to put other cigars with cello on either side. Also, spacers can be your friend as well. Like those you will often get in a box of tubo Romeo Y Juliettas.