There is some confusion over tempo. Tempo definitely affects the offense and I believe offense only.
That said, the by-product is still that the other team tires out quicker.
Playing a team that plays slowdown, if I play slowdown, my starters will all hit 32+ with decent stamina on fairly fresh.
Playing a team that plays uptempo, press, if I play slowdown, my starters usually max out at about 25 with decent stamina on fairly fresh.
Thus, even though it only affects offense, the effect of chasing around the faster offensive sets must tire out the opposing team quicker.