As far as I remember, there are also some quirks, mainly with combinations of what peripherals you have attached to the (single...) joypad port.
Magicoal is one game that supports nearly every peripherals that you can plug in there (Princess Maker 2 is another). It supports the MB128(saves its own game only, not backing up contents of backup RAM), multitap(as it has 2P co-op gameplay), 6-button pads and even the mouse! BUT every time I saved my game to MB128, it couldn't be loaded back (game frozen like the Emerald Dragon case mentioned here), but if I move the save back to the internal BRAM it works. I never figured out what's the problem, until recent years, that I've read somewhere online (sorry, can't find it now) that there is a bug in the game, so that when the multitap and the MB128 are both connected saved games in the MB128 cannot be loaded, i.e. there are some conflicts with some combination of peripherals(I think that's it, as my memory isn't good). Maybe there was a later revision of the game that fixed this glitch (like the recently confirmed fixed Altered Beast), it's frustrating anyway. Maybe Emerald Dragon has similar problems.
I think Lemmings even came with a small piece of paper insert warning players that the game won't work if the MB128 is connected. That is, they found a bug, but couldn't fix it before release. (Another game with funny paper insert was the extremely buggy, awesome, and extremely buggy awesome Monster Maker (I). The paper outright warned players not to save any game at certain location as that would make the game unwinnable. This is not MB128 related but isn't it cute?
). At least this game doesn't use the MB128 anyway, so just remember to remove it from the chain before you control the suicidal rodents. But in Magicoal's case the game actually supports both peripherals but couldn't use them at the same time. Again it's preferable to have the MB128 removed as its saves aren't that large to require it anyways and that 2P co-op is one of the main highlights of the game.
It's a pity they put the nail on the coffin to the original expansion port since the release of Duo, as 100% of the time that was eventually used to connect to the (interface unit of) CD-ROM drive anyway, leaving you with one single JOYPAD port to daisy chain connect with EVERY.SINGLE.EXPANSION.
Even if it's a slight change that the console came with two joypad ports would have saved a lot of troubles. Plus, it looks horrible as the chain of expansion stuff is a
literal chain. In the extreme case, typical setup of my system BiTD would be like:
_______________________
|Duo | |
| | |
| | |
|__________|__________|
|
___|___
|MB128|
|_____|
|
___|___
|MTap |
|_____|
/ | \
/ | \
P1 P2 Mouse
And not infrequently, when you move a bit harder, these stuff just fell off the table. NICE.