TAB can be represented in different ways by different text editors. For example indent of your program code may look different when opened by someone else using different text editor. From this reason it may be useful sometimes to convert / substitute all TAB's into uniform numbers of spaces.
perl -p -e 's/\t/ /g' tab-file.txt > no-tab-file.txt
sed 's/\t/ /g' tab-file.txt > no-tab-file.txt
both commands above depending on the version of sed will replace TAB's with 5x space character.