I'm still a newbie on groups.io but I have already found the need to scroll the 'Your Grouops' drop-down mildly irritating. Not that it's a serious problem, there are far too many seriously good features to be put off by a little scrolling :-)
My thought, but it may not help others with this concern, is that it might be useful to have (or to have an option to have) only groups listed in the drop-down and to have subgroups on a side menu from the group name. I only have a small number of groups, I appreciate that many others would see little benefit from such a change.
Malcolm.