Hello dennycm, we are glad you are part of this community
SDWAN purpose is to load balance traffic based on different SLA Targets and to provide redundancy.
Mainly the sessions are load balanced between sdwan interface members depending on your SDWAN rule configuration.
One session cannot use two outgoing interfaces, so doubling the speed of a single session using SDWAN is not possible.
Applications that use multiple streams (sessions) that can be load balanced between SDWAN interfaces benefit the most throughput wise.
You can check the following administration guide for configuration samples with different SDWAN rules:
"Serenity now. Insanity later"