When you compare the cost of modern fractional bullion to whole ounce bars, coins and rounds, you'll notice the premium is beyond excessive. After doing the math, you'll find that you're paying at least an extra $10/oz per ounce of gold, silver, etc. While they can be fun to collect, it's not practical to stack large quantities.
At some point in each country's history, coins were primarily made of silver and gold. When this stopped will vary by country, but many coins prior to the 1960s were largely made of silver, ranging in purity from 30 to 95%. Not only are the coins intrinsically valuable, but they are minted in denominations easily recognizable by others.
Fractional Bullion for Bartering
One advantage of fractional bullion would be for use in barter, rather than selling off small piece for spare cash. While the possibility of a global economic collapse seems highly unlikely, it's also not an impossibility. If you're one who likes to have your bases covered, it's not a bad idea to have some fractional bullion. Fractional silver is the best suited for barter purposes, and fortunately there's an alternative to modern bullion.
Fractional Bullion for Investing
One aspect to also consider about fractional bullion is it also presents an investment opportunity. The coinage stopped being made with gold and silver, so what is left in circulation is all that will exist. You can sometimes find lower mintage years that are worth even more because of collector demand. Because no more will be made, even non-collector coins will increase in value as some are inevitably scrapped for their melt value. If people want it they'll have to pay more to get it, since it's not being made anymore, and those who have it won't be willing to part with it for average bullion prices.
So whether you're planning for a possible need to have precious metals for barter or as an investment, fractional bullion is an excellent addition to your stack when done in moderation.