SQL Rebuild indexes data size percent a little smaller
SQL Server Internal Fragmentation is caused by pages that has too much free space. for example at the beginning of the day we have a table with 50 pages that is 100% full, but by the end of the day we have a table with 60 pages that is only 80% full because of various delete and insert statements throughout the day. This may lead to a decrease in performance because now when we need to read from this table we have to scan 60 pages instead of 50. Index maintenance tool and additional information here.