There are implicit measures and explicit measures. The reasons I recommend you writing your own explicit measures are
1. You can set a permanent relevant business name like Total Sales, which is better than “sum of value”
2. You can set permanent relevant formatting, like $0.00
3. Your measures can be used inside other measures, like Average invoice value = [Total sales]/[Count of invoices]
4. When you learn to write dax, you get stronger and better at your craft.
If you drag a column as an implicit measure, you will always have limited ability.
