We're encouraged to allow our intermediate partners to attend any call and do any skill that is within their scope of practice. So to answer your question, yes the I's can attend a decent amount of patients.
They have a list of IV and PO meds they can give and attend the patient. They've also got a fair share of skills they can do.
I've never worked P/B, only P/I but I love having an I as a partner. Our county doesn't allow B's on ambulances.
My normal partner takes borderline ILS/ALS patients all the time, but she also has a bio degree, another science degree, scored a 36 on the MCAT (turned down three different med schools, don't ask me why) and is a senior year BSN student so she's a little different. Honestly knows more than I do about medicine, a lot more actually. I bring the skills and scene management to the party
It depends on the partner though, some medics take almost every call, I like to let them "play". I worked with medics when I was an I that all they let me do was carry bags, start lines and drive so I know how much that sucks to be treated like that.
We have to be able to split the calls. On days where everything is ALS it's not unusual for me to be charting for 2-3 hours after my scheduled EOS, we run so many calls no medic would want to work here if they had to attend everything.