@Dan **********
That would only have a benefit once your visa has expired but your entry stamp hasn’t. Say for instance your visa expires 1st November 2029 and you enter thailand one day before that, you still get stamped in for 180 days, and the only way to keep that stamp active if you leave the country again, would be to get a re-entry permit before you left.
During the validity of the visa, a re-entry permit just restricts your length of stay to the stamp you got before you left with the permit; ie it has no useful purpose.