Most people won't notice a difference, but when you're adding anything over 20 choices in a flow step, Marketo becomes really slow. I believe this lagging is due to the fact that it is auto saving every time a change is made. With really long or complex flows, this means this process takes a lot longer. It's currently taking over 30 seconds per additional flow step for me.
To recreate this, try adding a flow step such as "Change data value" and try to add 100 choices to it. You'll start to experience performance issues at around 20-30.
It would be great to be able to turn off auto saving - just temporarily - so I could create the entire flow and then save it.