Anyone registered to vote can choose a Republican or Democratic ballot. Many of the people on the Democratic ballot (in my area) are running unopposed, so it was a good opportunity to try to get the least crazy people on the November ballot. Also, the republican ballot has 13 propositions that are not on the Democratic one, so that’s your only chance to have a say in those (and IMO they are really really bad!)
Only for primaries I believe. There’s nothing stopping you from voting for the Republican primary then voting for Biden in November, or vice-versa.
This is true. I’ve done this countless times in Texas because I’ll vote for whatever democrat in the general election, but I want to do what I can to influence the republican primaries. Ironically I get so many mailers and calls from republican aligned groups that are scratching their head when I mention I’m gonna vote democrat in the generals.