I do have a misunderstanding between cash basis and accrual basis , when firms chose to apply one of these basis and depending on what ,?

In cash basis accounting, revenue recognized when cash is collected and expense is recognized when cash is paid. However, in accrual basis accounting , revenue is recognized when goods are transferred and services are rendered and expense is recognized when goods are received and services are obtained.    

CASH BASIS ACCOUNTING:

REVENUES are recognized when cash is RECEIVED

EXPENSES are recorded when cash is PAID

ACCRUAL BASIS ACCOUNTING:

REVENUES are recognized when EARNED

EXPENSES are recorded when OCCURRED