In which situation we should avoid using Future method in Salesforce?

Hi,

Future Apex. - Future Apex is used to run processes in a separate thread, at a later time when system resources become available. Note: Technically, you use the @future annotation to identify methods that run asynchronously.

A future method runs in the background, asynchronously. You can call a future method for executing long-running operations, such as callouts to external Web services or any operation you’d like to run in its own thread, on its own time. You can also make use of future methods to isolate DML operations on different sObject types to prevent the mixed DML error. Each future method is queued and executes when system resources become available. That way, the execution of your code doesn’t have to wait for the completion of a long-running operation. A benefit of using future methods is that some governor limits are higher, such as SOQL query limits and heap size limits.

Hope this helps.