What previews should I enable?

[luafyn via Digitalmars-d-learn]

Hi everyone, so dmd includes several -preview flags and I was 
wondering if there were any that are recommended to enable?

I like using the most up to date stuff possible so I've actually 
been using -preview=all and it seems to work alright, but then I 
hit a weird issue with sumtypes and -preview=dip1021 so I'm 
wondering if that's a bad idea.

Some of the previews seem pretty ok to use like the bugfix 
previews but I'm not sure about the DIPs. Like, is it required 
for me to use -preview=dip1000 to have `scope` do anything, for 
example? Cheers!