In my model of parenting, one of the most important things is that your kid can predict how you're going to respond to things. Otherwise you get:

• Asking a lot: if you say yes 5% of the time at random when asked for candy the best strategy for getting candy is just to ask over and over again.

• Testing: they'll try lots of things trying to find out where the yes/no border is, and the more complicated the border the more they'll try.

• Modelling effort: the kid is going to put a lot of effort into trying to model you in enough detail that they can predict your responses. While some of this is good practice, my feeling is that kids are already effectively overtrained on modeling their parents and later have to correct for overfitting.

• Generally unpleasant: there's so much unpredictability in their lives already relative to an adult in the same situation because they have so much less figured out. I don't want to make this worse!

Relatedly, you don't want them to start predicting things like "if I throw a tantrum then they'll say yes." Kids are super smart in some ways, even kids under two, and noticing connections between what they did and whether they got the outcome they want is one of the ways they're smartest. If you are persuaded by whining, begging, crying, incessant asking, sulking, or yelling, you're going to get a lot of that. Not only is that unpleasant for you, it's unpleasant for them: at a low level they know that if they put themself into this painful state they'll get something they want more than they dislike being in that state, but that doesn't make being in that state nice for them.

It's also really important to limit your use of commands: once they'll consistently follow requests it's tempting to use that a lot, but that's not fair to them or good for their development as an independent person.

(In general, I try to avoid using commands or making absolute statements about something I'll be doing. For example, if they ask me to read and I don't want to I might say "I don't feel like reading right now." This lets them know it's ok to try to convince me. If there's a deeper reason I try to give that: "sorry, I can't read to you right now because I need to cook dinner" gives them more information about how I'm thinking about it, and sometimes lets them figure out an alternate request I would say yes to.)