If you remember that a single thiokinase reaction is all it takes to make Acetyl CoA from acetate you can see that wherever the TCA cycle is operative acetate is just one step away from being able to be used as an oxidizable substrate. Clearly therefore in ruminant tissues acetate is able to substitute for much of the glucose that non-ruminants use for oxidative purposes in aerobically respiring cells.
Acetate can not replace glucose as an oxidizable substrate in the erythrocyte because glycolysis is necessary as the sole method for generation of ATP in erythrocytes.
Acetate can however replace glucose as the principal substrate for fatty acid biosynthesis in adipose tissue, liver and the lactating mammary gland. But remember that some glucose will always be needed in these tissues to make the glycerol phosphate used in lipogenesis to esterify the fatty acids. Fat synthesis requires glucose even if fatty acid synthesis doesn't.
Importantly also you have to think about other functions of glucose than its use an oxidizable substrate for which acetate can not serve as a replacement.
For example glucose is used to make other sugars; fructose is synthesised
in liver as an oxidizable substrate for use by the developing foetus and
galactose is synthesised in the lactating mammary gland for secretion into
the milk as a nutrient for the neonate. Acetate can not replace glucose
for either of these functions. Glucose is also indispensible for
making ribose sugars that are required for nucleic acid biosynthesis (in
all replicating cells) and for making monosaccharide osamine and uronate
derivatives used in the synthesis of proteoglycans (fibroblasts and other
cells that make extracellular polymers found in connective tissues).