Not necessarily. For example, in Ethiopia, no applicant in this forum has been asked for AoS(I-134). The COs strictly ask the relationship of applicants with their hosts. This is one way of checking the issue of public charge (strong relationship indirectly indicates the applicant won't be a public charge). They also ask previous work experiences. It may help them to judge if the applicant has enough saving to support oneself. This is in Ethiopia.
On the other hand, I saw two cases put on AP in UAE for not presenting AoS at the time of interview.
It depends on the specific requirement of the embassy.
But, in general, if you can get AoS, it is good to make it ready. The second option is to show bank statement of your savings. The third option is to show documents of your personal assets, like vehicle and house. You can also combine bank statement and personal assets. They can replace AoS.