Almost all workbooks in Excel are saved in the file type XLSX. However, other file types in Excel, including XLSM and XLSB. When you use the Save As a function, you will be asked the folder and file name.
The question to ask yourself is, which file type should I use? Default by Excel sets XLSX, but you can still change to another file type used at that particular time.
The XLSM format type
You will be asked to change your file extension to XLSM if you have VBA macros in your XLSX file. The XLSM file type has the default Excel file type for workbooks within VBA. Therefore, save your macro within this file format. It is beneficial since it can use up to 2^20 (1048576) rows plus 2^14 (=16384) columns. This file format uses the open file format, making it accessible to other applications.
XLSM file format uses the open XML standard. It also saves and uses all the functions that are available in Excel. However, it is unsafe since it contains malicious codes in the VBA part. The XLSM file format requires more disk space than other formats like XLSB. It cannot be opened with the Excel versions before 2003. If your file uses VBA macros, you can use the XLSM file format. This format applies to files not more than 10MB.
In addition, if you want to save VBA macros programs so that your work can be made simple, use the XLSM file type. Most importantly, use the format with a trusted individual while creating the file. In this regard, you will avoid receiving malicious software.
The XLSB file type
The XLSB file format can be an alternative to the XLSM file format. However, it stores data more differently than the latter. This file format does not use the XLM file structure like the XLSM file format. The files here save disk space since the binary structure is used to store data. The major difference is that Binary files are computer read but not human readable. The XLSB can be used to store files of smaller sizes and is faster in opening and closing the files. The file format allows formulas with more than 8192 characters. It can also save all functions that are available in Excel.
Like the XLSM file format, the XLSB is also insecure since files can have VBA code. It is impossible to change the Excel ribbon for this file format, and tools such as OpenOffice will not open your file. Though this problem might have been sorted out nowadays, you still cannot open files of Excel 2003 and earlier. The file type is still not very popular; hence people are still confused about receiving XLSB files from you. Use XLSB file type if your files are larger than 10MB.