I have the habit of closing one project before I open the next.
Should I wake up, smell the coffee and realize it’s 2018 and have a few open?
It seems to work OK but I thought I ask before I change my habits.
Do people in general have issues when there are a few or a lot of projects open, small or large?
Horror stories? 
I always only have one project open unless I am copying tracks from one to the other. It always feels good when I finally close one of them.
Can’t say I’ve noticed problems other than me getting confused when I have more than one open but it’s not something I tend to do regularly unless as above I’m copying tracks from one to another.
It might take longer to shutdown if you’ve got lots of projects open (?) so I’d wonder why would you want to have lots of projects open and what do you expect to gain from it?
I’m merging a bunch of sketches into songs at the moment, so there are ingredients spread over the sketches that finally will land in the songs.
While I’m poking around with that I notice I close a lot of the sketches too soon and then I need to open them for some stupid reason e.g. check the tempo.
It just gets a little tedious … I think I will have to try to see what happens.
It relatively small projects with a few guitars, maybe a guide vox, MIDI drums and bass, and an occasional keyboard
If everything explodes I’ll stop, if it doesn’t I’m good! 
Depends on the situation but in general I will only have one project open at a time, especially when working with external gear. I only see the need to have more than one open if there is a relevance like comparing certain aspects between 2 or 3 versions. To copy tracks I normally use the import function. Works like a charm.
Yeah, thanks! Amazing funstionallity.
It works in most cases but sometimes you need something that’s not a Track …
In that case I leaf another project open but preferably not more than 3 at a time. I also sometimes will set up a new project and first copy all the stuff I think I need at the end. So I don’t have to switch to another project. The ‘switching’ sometime interferes with my concentration or flow of the moment so I want to keep it down to a minimum.
When I’m getting close to finishing an album project, and tweaking and exporting mixes to quickly check on other playback systems, I may have several projects open. When you switch to (activate) another project you’re just loading the mix console, rather than the whole project, so it’s faster to return to a project. I have not noticed any downside to this, with 16G of RAM. When you do start closing out projects, you want to close the unactivated ones first, so you don’t start automatically loading a project you’re done with because you closed the activated one first.
I’ve only had 2 or 3 opened at a time for referencing instrument patches and effects. There’s been no complaints from CB although I prefer to have only one project open at a time. Haven’t had the need otherwise but I know it’s ok if need be. As pkf mentioned, you’re only reloading the mix console so there seems to be no system overloading.