We use the present perfect continuous when the focus is on an activity that is unfinished.
I’ve read that book you lent me. I finished it yesterday.
I’ve been reading that book you lent me. I’ve got another 50 pages to read.
The present perfect simple (I’ve read) gives the idea of completion while the present perfect continuous (I’ve been reading) suggests that something is unfinished.
She’s been writing emails for 3 hours.She’s written 10 messages.
The present perfect continuous (has been writing) talks about how long something has been happening. The present perfect simple (has written) talks about how much/how many have been completed.
I’ve worked here for thirty years.
I usually work in London but I’ve been working in Birmingham for the last 3 weeks.