Here's a breakdown of when to use IF functions or VLOOKUP in Excel:

IF function:

* Use the IF function when you have a simple condition to evaluate and need a corresponding output based on whether the condition is true or false.
* It's ideal for scenarios with limited criteria (usually one or two) to determine the outcome.
* IF functions are generally easier to understand and maintain compared to complex VLOOKUP formulas.

VLOOKUP function:

* Use VLOOKUP when you need to search for a specific value in a table (lookup table) and return a corresponding value from another column within that table.
* It's efficient for situations where you have a large dataset and need to retrieve data based on a lookup value.
* VLOOKUP can handle multiple criteria for searching within the lookup table (up to 255 conditions in newer Excel versions).

Here's a table summarizing the key differences:

| Feature | IF Function | VLOOKUP Function |
|------------------|---------------------------------------------|-------------------------------------------------|
| Use Case | Simple conditions and single output | Lookups in a table and retrieving data |
| Criteria | Limited (one or two conditions) | Multiple criteria (up to 255) |
| Complexity | Easier to understand and maintain | Can be complex for beginners |
| Data Structure | Not applicable | Requires a well-defined lookup table |

In simpler terms:

- Use IF for "If this happens, then do this, otherwise do that" situations.
- Use VLOOKUP for "Find this value in a table, then give me the value from another column in that table" situations.

Example:

* IF function: Assigning a grade based on a score: `=IF(A1>=90, "A", IF(A1>=80, "B", "Fail"))`
* VLOOKUP function: Finding a product price based on its ID: `=VLOOKUP(B2, A1:C10, 3, FALSE)` (assuming product IDs are in A1:A10, prices are in C1:C10, and you want the value from the 3rd column)

Ultimately, the best choice depends on your specific needs and data structure. If you're unsure, start with the IF function for its simplicity. If dealing with lookups in a large table, VLOOKUP might be more efficient.