This is a low-pressure way to tell someone what to do. You use this phrase when you're training someone, giving them directions, etc. but you don't want to seem too bossy.
Here are some examples:
You probably want to get into the left lane. You're going to need to turn soon.
You probably want to get going now. It's almost nine.
You can also use the future tense version:
You'll probably want to get a better pair of skis if you're going to be skiing a lot.
This phrase sounds friendly and casual.