The problem, I've found, is players who are unable to articulate a course of action because they don't have a firm grasp of the rules, and then get bogged down in the action economy minutiae. I'm not usually the DMs in these games, so I generally have to grit my teeth over it.
You've never had fun conversations like this?
Player: "I want cast bless on the myself and my 3 friends here, here, and here."
DM: "Ok, that's 4 people, you'll need to spend a 2nd level slot for that."
Player: "Oh, wait....I don't have any more 2nd level slots."
DM: "Well, you can use a 1st level slot, and just bless 3 people."
Player: <thinks for 10 seconds>
Player: "Can I use a 3rd level slot instead? I have those."
DM: "Sure, if you use a 3rd level slot you can bless 5 people."
Player: "5 people, OK." <thinks, looks around at board>
Player: "I'll bless her, the PC over there".
DM: "Well, actually, she's out of range. Needs to be within 30'."
Player: <thinks for 10 more seconds>
Player: "Well, I can't bless everyone, so I guess I'll just bless 3 people for a first level slot."
DM: "Ok, sounds good. Just remember it's concentration if you get hit.
Player: "Oh, it's concentration? That's not good, I have a concentration spell up already. I'm going to do something else..."