As it was explained to me, you set the app to pool. When you pick up a pax that's pool riding, you are off to their destination, if someone along that route that is going the same way pings in, you pick that pax up. Drop off pax 1, continue on with pax 2 and then pax 3 can ping you and so on... It can be a contiguous ride but it could also end with pax 2. Riding pool will be slightly cheaper for the pax but it should not affect your pay.
When I lived in another city that had pool as an option it was an absolute nightmare. You don't make much on pool rides when you take into account having to pick up another pax along the way, sure it can turn into one long ride but the pool rate will be less. Also, what the pax will not understand is that is going to take them longer then expected to get to their point of travel depending if someone else that is pooling is closer. Do not opt in.
I haven’t seen anyone who likes UberPool. Riders take it because it’s cheaper, then some don’t understand it and why you’re picking up others. Some get unhappy and then ding your rating. Plus, if there are willing to go UberPool for less, do you really think they’re tippers?