BPMN gates.

Hello all, I am new in BPMN just started learning.

I am confused in basic things.. or I have some basic questions.

Q1: why we should avoid OR gates in BPMN? (in some books they referred we should avoid OR gates)

any reference or any example.

Q2: where XOR split is useful than OR Split and where XOR join is useful than OR Join and vice versa.

any explanation with example. which i can easily understand.

Please help me out.