When exporting JIRA issues to Excel, it exports files in XLS files. The same occurs for exports to Word, which generates files in DOC format. These files have multiple disadvantages when compared to the new file types introduced by Microsoft in 2007 (DOCX, XLSX and PPTX). That's because those new file formats are XML-based, which allows for much better compression, resulting in considerably smaller files.
Also, Excel's new file format (XLSX) adds an extra layer of security by blocking the usage of Macros, which requires the file to be saved as XLSM. XLS files allows for any Macro to be included and is being blocked by multiple System Administrators, especially in companies with higher standards for security.
Exporting around 4900 issues to Excel from JIRA currently generates a file with an approximate size of 7.5 MB. If we convert that file to XLSX once it has been opened in Excel 2007 or later, the file size drops to less than 10% of the original file's size.
The Better Excel Plugin, developed by Midori, adds additional features for exporting issues to Excel in JIRA, including the ability to export directly to XLSX.
Please note third-party add-ons, such as "Better Excel Plugin", are not supported by Atlassian. Therefore, support and maintenance is purely responsibility of the add-on's vendor.